The American government as a whole--the judicial, legislative, and executive branches, and the countless others that are part of the governing body--is, for the most part, set-up to deter a 'slacker' mentality.  The system of checks and balances helps immensely in this field.  Checks and balances were put into place by the Founding Fathers of this country, and help to ensure that our elected governing officials don't get too power hungry, and the contrary of that.  Congress and the president tend to take a very active role in most things politics.  However, they are only humans, and all humans become apathetic about something, at some point in their lives.  I am not condoning the disinterest that plagues our elected officials, but I am saying that 'it happens'.  With that said, for a congressman or president to stop fulfilling their duties to the best of their ability, could be dangerous.  They are the ones that pass the laws, correspond with other world powers, and essentially watch over us to ensure that justice is fully executed.  They are the ones that wage wars and protect us from imminent danger, and ensure that things are running smoothly within the country as a whole.  For them to simply stop performing the duties that allow the aforementioned to happen, is simply not okay.  

Congress is the easiest place for an elected official to become lazy.  The House of Representatives, with 435 members, often times goes unnoticed.  They are not in the media that often (unless you're watching C-SPAN), and if they are, generally they are not named personally.  This makes it very easy for a member of the House to become lazy, and stop performing their duties fully.  The amount of bills that they see every day, and have to give their opinions on, is daunting at best; after all, these are the bills that will become laws to keep their constituents in check.  Dealing with this work load cannot be easy, and simply abstaining from voting and instead marking 'present' could be a lot easier than making a decision on a certain issue.  In the Senate, it is more difficult to 'slack' on the job, however.  Anyone who watches the news will know that Senators are generally made fairly public (some more than others).  This makes it very difficult for Senators to abstain from voting, or something of the sort.  Congressmen also are allowed to hire a staff who do the majority of research on issues for them.  This allows the congressmen to sit back, relax, and simply read what their aides have provided for them (it's not as easy as I made it sound, though).  This system has the potential to allow congressmen to do less work, and should they choose, do little to no work.  Committees also allow congressmen to do minimal work, unless they are on a committee (which most congressmen are).  There are certain committees for certain issues (ie. agriculture, commerce, etc...) and they do the coaxing when it comes time to get their legislation passed.  This allows the other congressmen to simply listen to their colleagues and base their decision off from what they are told.

The President is the least likely, and least able, to slack while on the job.  In the political world, the President is the most prominent and influential person.  They are perpetually showcased in the media (especially with our current President), and don't really have the option of slacking.  There are times, however, when pressing issues are somewhat trivial, and the President can take a 'back-seat' while in office, but for the most part, the President must come to work, with a vengeance, everyday.  He/she is probably the most watched person in America, and cannot afford to simply not perform their job, especially if they are looking for reelection.  If a President is in his lame-duck stage, however, they generally work a little less hard then they have in their previous years as President.  Take George W. Bush, for example.  In his last couple of years as President, things went terribly awry, and in his late months as President, it was clear that he was ready to relinquish his powers, and hand over the mess of a nation that he made to Barack Obama.  This is not typical, however.

Overall, while it is difficult for someone in our governing body to not perform his or her duties, it does happen, especially with the more obscure jobs.