Politico details the Republican turn against cap and trade:

Sen. John McCain (R-Ariz.), under pressure back home from a conservative primary challenger, hasn’t come anywhere close to the climate issue that was once a key component of his “maverick” credentials.
Sen. Lisa Murkowski (R-Alaska), who joined Sen. Jeff Bingaman (D-N.M.) on cap-and-trade legislation in 2008, challenged the Obama administration earlier this month by forcing a floor vote that would have removed EPA’s authority to write its own carbon rules.
Sen. Judd Gregg (R-N.H.), who has previously supported carbon limits on power plants, told reporters last week, “Nothing is going to go anywhere in this climate, as we go toward an election, that involves cap and trade.”
And Sen. Lindsey Graham (R-S.C.) halted climate negotiations with Sens. John Kerry (D-Mass.) and Joe Lieberman (I-Conn.) in April over concerns about immigration.
Cap-and-trade supporters hope Obama can turn around some Republicans — and get more Democrats on board — at a meeting with senators at the White House on Tuesday.
But when it comes to Obama’s overtures, recent history isn’t encouraging.
After meeting with the president earlier this month, Sen. Scott Brown (R-Mass.) said, “I told him I am not in favor, nor could I support, a national energy tax or a cap-and-trade proposal.”
While serving in the Massachusetts Legislature, Brown voted for the Regional Greenhouse Gas Initiative, which capped emissions from power plants. But he has since shifted to the right, going so far as to question the science linking humans to global warming.

Liberals have been making this point a thousand times, but it's worth reiterating. You can't think of this problem in personal terms. The issue here is not that Republicans are putting politics ahead of what they understand to be the national interest. Electoral politics incentivizes politicians to maximize their political power. That's what Republicans are doing. The problem is that the system also gives them the power to obstruct the majority's agenda.

In other words, the system, in order to function properly, requires politicians to be saints. Well-designed systems don't do that.