If Democrats cant hold the Senate with Gingrich as the GOP nominee.....

[Mr.Phips]

The Democratic party is clearly dead at the Congressional level.

If Gingrich is the Republican nominee, he will be lucky to break 150 electoral votes, meaning that he will likely lose pretty much every state where there is a competitive or Democratic held Senate seat with the exception of Nebraska. 

If Gingrich is the nominee, Democrats should be able to hold all of their own Senate seats except for Nebraska and pick up Massachussetts and Nevada and maybe even Arizona. 

Never in history has a party lost more than three Senate seats while their candidate was winning reelection to the White House. 

[○∙◄☻¥tπ[╪AV┼cVê└]

The Democrats can win a majority of the Senate seats up this year and fail to hold the Senate.

[Mr.Phips]

The Democrats can win a majority of the Senate seats up this year and fail to hold the Senate.

Most of the Democratic seats up are in states that Obama is likely to win. 

[Snowstalker Mk. II]

Democrats will hold the Senate. The only two likely pickups are NE and ND, and we can negate that (or even hold back a majority if the GOP gains more) by taking MA and/or NV. If Obama wins a 1996-like victory, he'll probably win or come within an inch of winning Missouri, so the more moderate (and whiter) McCaskill wins (I think she'll hold on unless it's an outright GOP victory). Kaine will win Virginia, Heinrich New Mexico, Brown Ohio, Nelson Florida. The only other seat left is Wisconsin, which may hinge on the recall election this summer.

[redcommander]

A Gingrich nomination is pretty much the only scenario where Democrats actually make net gains in the Senate. Even Santorum as the nominee would still keep the GOP's chances high of taking back the majority.