01/09/2012 04:18 pm ET Updated Jan 09, 2012

Mitt Romney Blowout Could Help Senate Democrats, Memo Says

WASHINGTON -- Mitt Romney could help Democrats keep control of the Senate by sewing up the Republican presidential nomination quickly, some Democratic strategists hope.

Chief among those are advisers to Rep. Joe Donnelly (D-Ind.), who is running to challenge incumbent Republican Sen. Richard Lugar and who sees a better shot at winning that Senate seat if the well-known Lugar loses a May primary to state Treasurer Richard Mourdock, a Tea Party candidate.

A Donnelly campaign memo obtained by The Huffington Post notes that Lugar's job approval rating has hovered around 42 percent lately, making him vulnerable to a primary challenge. But being better organized and more established than Mourdock, Lugar likely retains the edge if the Indiana primary becomes a high-interest, high-turnout affair, pushed along by an ongoing presidential nomination contest.

That's where Romney comes in, should he trounce his opponents in Tuesday's New Hampshire primary and ride the momentum through the next several states. By the time the later primaries occur, the presidential nomination contest could be all but over, leaving behind only those voters who care the most about electoral politics. They tend to be activists, and on the GOP side, they include Mourdock's Tea Party base.

"If the Republican nomination is sealed by the time Indiana's May primary rolls around, low turnout may prove a significant factor -- and a real challenge -- for Lugar," argues the Donnelly memo, prepared by the Global Strategy Group. "Lugar's success is largely dependent on a higher primary turnout, where the ideological bent of the voters is more mixed. In a low turnout election, Tea Party voters, who favor Mourdock, would dominate the primary."

According to Global Strategy Group's surveys last month, Mourdock and Lugar are statistically tied (42 to 41 percent) among GOP voters who took part in the last two primaries.

But if Romney is seen as a lock at the top of the ballot, Tea Party voters in particular could be inspired to turn out. Call it a Romney effect. "They are so effing pissed about Romney, they aren't going to settle anywhere else -- certainly not for Lugar," a Democratic operative said.

The hope for Democrats in Indiana is that the more conservative Mourdock would then alienate moderates and independents in the general election, giving Donnelly, a conservative Democrat, a chance in a state where a similar Democrat, then-Rep. Brad Ellsworth, was handily beaten in 2010 by now-Sen. Dan Coats, a former Republican congressman.

Indeed, Global Strategy Group's data -- which should be taken with a grain of salt because it was gathered for Donnelly -- finds Donnelly leading Mourdock by about seven percentage points.

Beyond Indiana, there are other races where Democrats hope a Romney effect could boost Tea Party candidates, presenting Democrats with opponents they might defeat and decreasing the odds the GOP can pick up the four seats it needs to take over the Senate. Among them are Nebraska (where Democrats are in deep trouble with the retirement of Sen. Ben Nelson), Michigan, Wisconsin, Missouri and, lately, even Virginia, where GOP favorite son and former Sen. George Allen could face a challenge from state Del. Bob Marshall.

Strategies that depend on such complicated ripple effects often prove unsuccessful, and Republicans point to 2010 general-election victories by such Tea Party favorites as Sen. Rand Paul (R-Ky.) and Sen. Marco Rubio (R-Fla.), who both won primaries over more moderate Republicans.

"Perhaps if national Democrats had spent more time focusing on their own races and on an agenda that is supported by a majority of voters, rather than spinning meaningless Republican primary narratives, they wouldn't have lost seven Senate seats and control of the U.S. House last cycle," said National Republican Senatorial Committee spokesman Brian Walsh. "It is amusing though to watch them do the same thing again in 2012."

Democrats respond by noting Republican losses in 2010 in Delaware (Christine O'Donnell), Nevada (Sharron Angle) and Colorado (Ken Buck) as evidence that Tea Party candidates can help them.

Michael McAuliff covers politics and Congress for The Huffington Post. Talk to him on Facebook.