The Senate

In the context of why it's hard for Obama to pass legislation (like the climate bill) in spite of his "mandate", Yglesias is right:

Dianne Feinstein, Barbara Boxer, Chuck Schumer, Kristen Gillibrand, Bill Nelson, Dick Durbin, Roland Burriss, Arlen Specter, Bob Casey, Sherrod Brown, Carl Levin, Amy Klobuchar, Kay Hagan, Bob Menendez, Frank Lautenberg, Mark Warner, Jim Webb, Patty Murray, Maria Cantwell, Ted Kennedy, John Kerry, and Evan Bayh represent 50 percent of the country’s population. But that only adds up to 22 Senators—you need thirty-eight more to pass a bill.
[...]
The American presidency is a weird institution. If Barack Obama wants to start a war with North Korea and jeopardize the lives of hundreds of thousands of people, it’s not clear that anyone could stop him. If he wants to let cold-blooded murderers out of prison, it’s completely clear that nobody can stop him. But if he wants to implement the agenda he was elected on just a few months ago, he needs to obtain a supermajority in the United States Senate.