6:40 p.m. Keith Olbermann asking questions of Andrea Mitchell, stationed at Clinton campaign headquarters in Ohio: Mitchell slips in that Bill Richardson is going to endorse Obama.

Olbermann interviews John Kerry, who has already endorsed Obama. Kerry is good on prospects for the Dem race from here on out, incl the point that it is mathematically almost impossible for Clinton to close her deficit in delegates, if the primaries are close tonight, even if she wins.

Exit polls turn up a nasty detail: in Texas, which permits crossover voting in its Dem primary--allowing Republicans to pick the Democratic candidate they want--there is a bigger GOP crossover vote in this year than there was in 2004. In Ohio, conversely, the crossover vote is smaller in 2008 than it was in 2004. Big turnout in both states, weather or no weather.

7:00 p.m., and the polls are closed in Vermont. NBC instantly calls Vermont for Obama--no surprises in that, as far as it goes. O'Donnell calls Vermont "an incredibly liberal state." Fifteen minutes later, at least Tim Russert has the grace to point out that it is also a white state. No hard numbers sufficient to determine the vote count, this early.

Andrea Mitchell and Chris Matthews canvass the question of whether Clinton shd drop out, again. Mitchell says that if Clinton were to lose both Ohio and Texas, there wd be no way for her to proceed.

Chris Matthews, with Olbermann, lays out the destructiveness of seven weeks in the six media markets of Pennsylvania, with the two Dems bashing each other. Still Matthews seems to be putting pressure on Obama to win all four states tonight. Odd.

Howard Dean laid out some good comments, succinctly, on McCain. Obama wd probably be wise to ignore Clinton and focus on McCain, as much as possible.

7:30 p.m. Polls close in Ohio. On the Democratic side, it is too early to try to call a result. McCain wins both Vermont and Ohio, as expected.