The White House says President Obama will meet privately with Sen. Blanche Lincoln Tuesday night.

Obama and Lincoln (D-AR) will huddle in the Oval Office at 5:15, less than two hours before polls close in the critical elections in New Jersey, New York and Virginia.

Lincoln is perhaps the most embattled Democrat in the Senate, and she's been getting political pressure from both sides as she declines to tip her hand on health care.

She is one of several moderates who have had the president's ear lately - Sen. Evan Bayh (D-IN), Sen. Jim Webb (D-VA) and Sen. Mark Warner (D-VA) also have visited the White House recently.

Speaking of senators who are keeping their options open, MoveOn has launched a new missive asking members to target Democrats who won't stand with the party to block a Republican filibuster.

In an email to 5 million members, MoveOn outlines a "nightmare scenario" where health care is stopped "because one Democratic senator joins Republicans to filibuster and block a vote."

"2009 becomes just another year when health care reform failed," MoveOn wrote.

They ask for members to pledge to chip in to help candidates who challenge any Democrat who won't vote for cloture in primaries.

"If the nightmare scenario happens, we'll encourage viable primary challengers to come forward, and if they do, make sure all of us who've pledged have a chance to support them," MoveOn wrote. "In other words, potential primary challengers will know there's a huge group of Americans who are ready to help. And conservative members of the Democratic Caucus will too."