But the professional handicappers say that although they still expect GOP gains, Democrats are slightly favored to retain their majority, and the majority party is likely to hold just 51 seats — or 50, with the vice president serving as the tiebreaker.
According to Rothenberg and Duffy, Republicans have some lackluster candidates, particularly in three Democratic seats that were expected to be easier targets: Missouri, Nebraska and North Dakota. Republicans continue to be hopeful about those three seats in large part because each of those states has grown increasingly Republican in recent years, putting the Democrats at some disadvantage.
A few key primaries will determine the slate of candidates, particularly in Nebraska and Wisconsin, where tea party activists are trying to rally opposition to GOP establishment figures.
Their strongest recruits are Rep. Denny Rehberg (Mont.), whose district comprises the entire state and is a well-known figure, and former senator George Allen (Va.), who nearly won reelection in 2006 despite running a poor campaign. Those two will face off against well-known figures, too: Sen. Jon Tester (D-Mont.) and former governor Timothy M. Kaine (Va.), making those two races potentially epic battles that could go down to the final days of the campaign as neck and neck.
Even if Democrats lose most of those seats, the biggest shift since last summer has been the emergence of opportunities for Democrats to pick up Republican-held seats in Maine, Massachusetts and Nevada. These would mitigate the losses on their turf, setting up the possibility of only the second 50-50 Senate in U.S. history.
Former Obama adviser and Harvard Law professor Elizabeth Warren has emerged as a liberal icon and her Senate race against incumbent Scott Brown (R-Mass.) has become a rallying point for Democrats far beyond Massachusetts. Warren has raised nearly $16 million since she entered the race eight months ago. Her missteps over her claims of Native American heritage have raised questions about how she will handle the day-to-day work of political glad-handing that Massachusetts voters are accustomed to, but her campaign will have abundant resources in a state in which Brown will have to outperform presumed Republican presidential nominee Mitt Romney by roughly 500,000 votes in order to win.
In Nevada, Sen. Dean Heller (R) and Rep. Shelley Berkley (D) are in a tight race that could depend on how well Obama and Romney do in that battleground state.
The biggest break for Democrats came with the surprise retirement of Sen. Olympia J. Snowe (R-Maine), who, despite her moderate views, faced no real challenge in her primary and was likely to cruise to reelection. Now, former governor Angus King, an independent, is running for her seat and most observers think he will win and caucus with Democrats.