Paul Krugman has a terrific column on the subject.

The fact is that one of our two great political parties has made it clear that it has no interest in making America governable, unless it’s doing the governing. And that party now controls one house of Congress, which means that the country will not, in fact, be governable without that party’s cooperation — cooperation that won’t be forthcoming.

This is demonstrably true over the past two years. And now the Republicans have given birth to a monster—the Tea Party People—that they can not control.

And opposition for the sake of opposition isn’t limited to economic policy. Politics, they used to tell us, stops at the water’s edge — but that was then.

These days, national security experts are tearing their hair out over the decision of Senate Republicans to block a desperately needed new strategic arms treaty. And everyone knows that these Republicans oppose the treaty, not because of legitimate objections, but simply because it’s an Obama administration initiative; if sabotaging the president endangers the nation, so be it.

A defining characteristic of American life has been optimism, but these days, it’s tough to feel hopeful.