What obstacles do the division of power present to enactment of important legislation?
The division of power among the branches of the US government (and within the Congress) make it much harder to get important legislation passed. The current situation is a case in point. To Republicans, the repeal of "Obamacare" is a huge priority. However, there is no way that they can possibly pass a law to repeal it. This is because President Obama is in the White House and could simply veto the law. Even if Mitt Romney becomes president next year, the Republicans might not control the Senate and will certainly not have the 60 votes they would need to get such an important bill passed. Because the House, Senate, and Executive all have to agree, it is very hard to enact important legislation.