Critics generally claim three basic disadvantages for presidential  systems:
 - Tendency towards authoritarianism — some political scientists  say that presidentialism is not constitutionally stable. According to  some political scientists, such as Fred Riggs,  presidentialism has fallen into authoritarianism in nearly every country it  has been attempted. Critics such as Dana D. Nelson in her 2008 book Bad for Democracy[2]  see the office of the presidency in the United  States as essentially undemocratic[3]  and she sees presidentialism as worship of the presidency by  citizens which tends to undermine civic participation.[3]
 - Separation of powers — a presidential system establishes the  presidency and the legislature as two parallel structures. Critics argue  that this creates undesirable gridlock, and that it reduces  accountability by allowing the president and the legislature to shift  blame to each other.
 - Impediments to leadership change — it is claimed that the  difficulty in removing an unsuitable president from office before his or  her term has expired represents a significant problem.
 
 Tendency  towards authoritarianism
 Winning the presidency is a winner-take-all, zero-sum prize. A prime  minister who does not enjoy a majority in the legislature will have to  either form a coalition or, if he is able to lead a minority government,  govern in a manner acceptable to at least some of the opposition  parties. Even if the prime minister leads a majority government, he must  still govern within (perhaps unwritten) constraints as determined by  the members of his party—a premier in this situation is often at greater  risk of losing his party leadership than his party is at risk of losing  the next election. On the other hand, once elected a president can not  only marginalize the influence of other parties, but can exclude rival  factions in his own party as well, or even leave the party whose ticket  he was elected under. The president can thus rule without any allies for  the duration of one or possibly multiple terms, a worrisome situation  for many interest groups. Juan  Linz argues that:
  The danger that zero-sum presidential elections pose is compounded by  the rigidity of the president's fixed term in office. Winners and  losers are sharply defined for the entire period of the presidential  mandate... losers must wait four or five years without any access to  executive power and patronage. The zero-sum game in presidential regimes  raises the stakes of presidential elections and inevitably exacerbates  their attendant tension and polarization.
 
 Constitutions that only require plurality support are said to be  especially undesirable, as significant power can be vested in a person  who does not enjoy support from a majority of the population.
 Some political scientists go further, and argue that presidential  systems have difficulty sustaining democratic practices, noting that  presidentialism has slipped into authoritarianism in many of the  countries in which it has been implemented. Seymour Martin Lipset and others are careful to  point out that this has taken place in political cultures not conducive  to democracy, and that militaries have tended to play a prominent role  in most of these countries. Nevertheless, certain aspects of the  presidential system may have played a role in some situations.
 In a presidential system, the legislature and the president have  equally valid mandates from the public. There is often no way to  reconcile conflict between the branches of government. When president  and legislature are in disagreement and government is not working  effectively, there is a powerful incentive to employ  extra-constitutional maneuvres to break the deadlock.
 Ecuador  is sometimes presented as a case study of democratic failures over the  past quarter-century. Presidents have ignored the legislature or  bypassed it altogether. One president had the National Assembly  teargassed, while another was kidnapped by paratroopers until he agreed  to certain congressional demands. From 1979 through 1988, Ecuador  staggered through a succession of executive-legislative confrontations  that created a near permanent crisis atmosphere in the policy. In 1984,  President León Febres Cordero tried to physically bar new  Congressionally-appointed supreme court appointees from taking their  seats. In Brazil,  presidents have accomplished their objectives by creating executive  agencies over which Congress had no say.
 Separation of powers
 Presidential systems are said by critics not to offer voters the kind  of accountability seen in parliamentary systems. It is easy for either  the president or Congress to escape blame by blaming the other.  Describing the United States, former Treasury Secretary C. Douglas Dillon said "the president blames Congress, the  Congress blames the president, and the public remains confused and  disgusted with government in Washington".
 In Congressional Government, Woodrow Wilson asked,
  ...how is the schoolmaster, the nation, to know which boy needs the  whipping? ... Power and strict accountability for its use are the  essential constituents of good government. ... It is, therefore,  manifestly a radical defect in our federal system that it parcels out  power and confuses responsibility as it does. The main purpose of the  Convention of 1787 seems to have been to accomplish this grievous  mistake. The 'literary theory' of checks and balances is simply a  consistent account of what our constitution makers tried to do; and  those checks and balances have proved mischievous just to the extent  which they have succeeded in establishing themselves ... [the Framers]  would be the first to admit that the only fruit of dividing power had  been to make it irresponsible.
 
 Consider the example of the increase in the federal debt of the  United States that occurred during the presidency of Republican Ronald  Reagan. Arguably, the deficits were the product of a bargain  between President Reagan and the Democratic Speaker of the House of  Representatives, Tip O'Neill - O'Neill agreed not to oppose tax  cuts favored by Reagan, and in exchange Reagan agreed to sign budgets  that failed to adequately restrain spending. In such a scenario, each  side can claim to be displeased with the debt, plausibly blame the other  side for the deficit, and still tout its own success.
  Impediments  to leadership change
 Another alleged problem of presidentialism is that it is often  difficult to remove a president from office early. Even if a president  is "proved to be inefficient, even if he becomes unpopular, even if his  policy is unacceptable to the majority of his countrymen, he and his  methods must be endured until the moment comes for a new election."  (Balfour, intro to the English Constitution). Consider John  Tyler, who only became president because William Henry Harrison had died after  thirty days. Tyler refused to sign Whig legislation, was loathed by his  nominal party, but remained firmly in control of the executive branch.  Since most presidential systems provide no legal means to remove a  president simply for being unpopular, many presidential countries have  experienced military coups to remove a leader who is said to have lost  his mandate.
 In parliamentary systems, unpopular leaders can be quickly removed by  a vote of no confidence, a procedure which is reckoned to be a  "pressure release valve" for political tension. Votes of no confidence  are easier to achieve in minority government situations, but even if the  unpopular leader heads a majority government, nonetheless he is often in a far  less secure position than a president. Removing a president through impeachment  is a procedure mandated by most constitutions, but impeachment  proceedings usually cannot be initiated except in cases where the  president has violated the constitution and/or broken the law.  Impeachment is usually made into a very difficult process, by comparison  the process of removing a party leader is governed by the (often much  less formal) rules of the party in question. Nearly all parties  (including governing parties) have a relatively simple and  straightforward process for removing their leaders. If a premier  sustains a serious enough blow to his/her popularity and refuses to  resign on his/her own prior to the next election, then members of  his/her party face the prospect of losing their seats. So other  prominent party members have a very strong incentive to initiate a  leadership challenge in hopes of mitigating damage to the party. More  often than not, a premier facing a serious challenge will resolve to  save face by resigning before he/she is formally removed—Margaret Thatcher's relinquishing of her premiership being  a prominent, recent example.
 In The English Constitution, Walter Bagehot criticized presidentialism because it does  not allow a transfer in power in the event of an emergency.
 - Under a cabinet constitution at a sudden emergency the people can  choose a ruler for the occasion. It is quite possible and even likely  that he would not be ruler before the occasion. The great qualities, the  imperious will, the rapid energy, the eager nature fit for a great  crisis are not required—are impediments—in common times. A Lord  Liverpool is better in everyday politics than a Chatham—a Louis Philippe  far better than a Napoleon. By the structure of the world we want, at  the sudden occurrence of a grave tempest, to change the helmsman—to  replace the pilot of the calm by the pilot of the storm.
 
 - But under a presidential government you can do nothing of the kind.  The American government calls itself a government of the supreme people;  but at a quick crisis, the time when a sovereign power is most needed,  you cannot find the supreme people. You have got a congress elected for  one fixed period, going out perhaps by fixed installments, which cannot  be accelerated or retarded—you have a president chosen for a fixed  period, and immovable during that period: ..there is no elastic  element... you have bespoken your government in advance, and whether it  is what you want or not, by law you must keep it ... (The English  Constitution, the Cabinet.)
 
 Years later, Bagehot's observation came to life during World War II,  when Neville Chamberlain was replaced with Winston Churchill.
 Finally, many have criticized presidential systems for their alleged  slowness in responding to their citizens' needs. Often, the checks and  balances make action extremely difficult. Walter Bagehot said of the American system "the executive  is crippled by not getting the law it needs, and the legislature is  spoiled by having to act without responsibility: the executive becomes  unfit for its name, since it cannot execute what it decides on; the  legislature is demoralized by liberty, by taking decisions of others  [and not itself] will suffer the effects". (ibid.)
 Defenders of Presidential systems, on the other hand, hold that this  can serve to ensure that minority wishes and rights are not trampled  upon, thus preventing a "Tyranny of the majority" and vice  versa protect the wishes and rights of the majority from abuse by  legislature and/or executive that holds a contrary view point,  especially when there are frequent, scheduled elections. It should be  noted however, that despite the veto of President Wilson, Congress and  the Senate still passed the National Prohibition Act which effectively  outlawed the sale, manufacture, and transportation of alcohol.
 British-Irish philosopher and MP Edmund  Burke stated that officials should be elected based on "his [or  her] unbiased opinion, his [or her] mature judgment, [and] his [or her]  enlightened conscience", and therefore should reflect on the arguments  for and against certain policies before taking positions and then act  out on what an official would believe to be best in the long run for  one's constituents and country as a whole even if it means short term  backlash. Thus Defenders of Presidential systems hold that sometimes  what is wisest may not always be the  most popular decision and vice versa.