Polls close in Michigan and Arizona at 9:00 p.m. Eastern; I’ll be back with a late wrap-up once the votes are counted. Meanwhile, plenty of good stuff to read:

1. Breaking the evening: Olympia Snowe will not seek reelection. Wow. Major hit to GOP chances for a majority in the Senate. Via the invaluable Taegan Goddard.

2. Really good reminder from Mark Blumenthal: primary elections remain difficult to poll, meaning that with Michigan a polling toss-up, “It would not be at all surprising to see either candidate win Michigan's popular vote by a significantly larger margin than forecast by the final polls.”

3. Nice piece from Jonathan Cohn, who is reporting from Michigan, that I missed last night, making the point I made today: there really isn’t much difference on public policy between the leading Republican contenders.

4. For whatever it’s worth, Josh Putnam notes that Romney is headed for a solid win in the ongoing Wyoming caucus straw polls. Hey, it’s another state, and the in-caucus straw polls are likely at least vaguely predictive of delegate totals.

5. Mitt Romney’s budget plans depend heavily on “dynamic scoring,” also known as transparently phony numbers. Will it work? Ezra Klein is not impressed.

6. Not just Romney — Paul Krugman shows that the Republican candidates would all produce larger deficits than Barack Obama, if you just take their plans and his current budget.

7. Romneycare vs. Obamacare, again, from Ezra Klein. Bottom line: if facts matter, Romney’s case that the two are fundamentally different won’t convince anyone.

8. Yes, Republicans are still, years later, peddling an out-of-context version of what Barack Obama said about U.S. “exceptionalism.” Despite that anyone who cares to knows the truth . . . well, it’s clear that Karl Rove, for example, isn’t interested, as Conor Friedersdorf explains.

9. Digby collects the latest on the various birth control controversies.

10. Speaking of which, Irin Carmon looks at the latest flare-up in Alabama, and sets it in the larger history of the abortion battles.

11. David Brooks railed today against those who enable the crazy fringe of the GOP, but Ed Kilgore notes that Brooks himself is frequently guilty of exactly that.

12. Andrew Sullivan on Obama and medical marijuana.

13. Jamelle Bouie chimes in on Obama’s UAW speech.

14. And Steve Benen on Obama’s speech: “the success of the president's policy [on Detroit] will be at the heart of his re-election effort.”