I'm trying to wrap my mind around the current situation in Washington, especially the interplay between Tea Partiers and establishment Republicans.
Conservative fans of "limited government" will be quick to mention the meme of "checks and balances." However, they seem to be focused on the check part of that phrase. For something to go down, you need a majority of both houses of Congress and the president to agree, with the courts getting to chime in if the law is of questionable constitutionality.
That gives each branch an effective veto on what happens in government. Congress needs a two-thirds majority of both houses to do things over the objections of the president and needs an additional three-quarters of the states if they want to overrule the Supreme Court with a constitutional amendment. Congress is well within its rights to say "hell, no" to stuff that isn't in the best interest of the country, checking any autocratic tendencies of the White House.
However, we also have the issue of balance in "checks and balances." The House is elected by various sub-regional districts every two years, which gives voters a quick way to change things and representatives that will go to bat for their district. The Senate is elected on a state-wide basis, a third every two years, giving both a less homogenous clientele and a moving average of public opinion over the last six years. The president is elected nation-wide (in state-by-state Electoral College races) every four years, the one official that has to represent a broad swath of the country in order to get elected rather than one state or a subset of a state.
Getting all three of those to agree will create a balance, not allowing one person or one moment in time to carry the day. That's a status-quoian framework, making it hard to make changes since it needs to get approved by different factions elected at different times and in different constituencies.
A parliamentary system can turn on a dime. If the Greeks want to elect a hard-left government that scraps austerity and tells the European Central Bank to do an unnatural act with itself, they can do so without having to wonder if it can get things passed the Senate or a presidential veto; at least, I don't recall the Greek governmental system to hae such road-blocks.
Washington is not designed to turn on a dime, unless the crisis at hand can create consensus enough to get everyone to sign off on that 180; a simple, 50.1% majority of one body isn't going to do the job with our Constitution.
That means getting the president on board, unless he is so out of step with even his own party to allow enough members of his party to dis him and create a 2/3rd overriding majority. That doesn't happen too often.
I'm reminded of a quip about tradition giving the dead a vote. The 2012 electorate isn't dead, but it gets a vote in our system in that they sent Obama back for a second term. Likewise, the 2010 electorate has its say in the class of senators elected that year and who will be up for reelection next year. Next year. they'll wind up replacing 2010 with 2016 in the moving average of the Senate.
That's how our system works. Tea Partiers might like to have a more majoritarian system that was 100% 2014, but a just-say-no check of the White House gets called for a cross-check that gives you a two-minute stay in the sin-bin. They might be able to get a veto, but Congress and the president need to hash things out, lest we want to revisit 1787's rules of the road and start from scratch with a new system.