Eight months before the Nov. 4 elections, Republicans have expanded the number of competitive races for U.S. Senate seats and have a growing chance of gaining control of that chamber and stalling Democratic President Barack Obama's second-term agenda.
Public dissatisfaction with the president, concerns about his healthcare overhaul and a sluggish economy, and a series of retirements by key Democratic senators in conservative states have made a rugged year for Democrats even more so, analysts and strategists in both parties say.
Republicans, who are widely expected to retain control of the U.S. House of Representatives, need a net gain of six seats to take back the 100-member Senate. Recent polling indicates they have big leads in three states - Montana, South Dakota and West Virginia - where longtime Democratic senators have retired or will retire in January.
Although the primary season is just starting and the candidates in many races are not set, polls suggest Republicans have boosted their odds of gaining additional Senate seats by becoming competitive in politically divided states such as Michigan and Colorado, where a year ago they were given little chance of winning.
Senate races in those states and five others now represented by Democrats - Alaska, Arkansas, Iowa, Louisiana and North Carolina - have been close in early voter surveys.
Democrats have a chance to pick up Republican-held seats in two states: Kentucky, where Senate Republican Leader Mitch McConnell is expected to dispatch a Tea Party-backed challenger in the primary but would face a tough fight against Democrat Alison Grimes in November; and Georgia, where Michelle Nunn, daughter of former Democratic senator Sam Nunn, will face the winner of a crowded Republican primary in a race to replace retiring Republican Saxby Chambliss.
That leaves Republicans needing to win at least three of the seven closely contested races for seats now held by Democrats, while holding off Grimes and Nunn in Kentucky and Georgia. If either of them wins in November, the task for Republicans will be more difficult.
"It's moving a little in the Republican direction," said Larry Sabato of the University of Virginia. His Crystal Ball website rates the Senate as a toss-up. "Republicans will pick up Senate seats, probably three or four. The question is, will they get that wave in October that carries them to the six they need?"
CONCERN AT THE WHITE HOUSE
If Republicans were to control the Senate and the House for the last two years of Obama's presidency, virtually any legislation or nomination he sought from Congress would probably be frozen in place.
Republicans also would be likely to press the Senate to join the House in trying to dismantle the Affordable Care Act, known as Obamacare. Although Obama could veto any bill from Congress that targets it, a Republican takeover of the Senate would put him on defense for the balance of his tenure.
There have been signs that Obama's administration is increasingly concerned about the 2014 elections.
This week's decision by the White House to extend the time insurers can offer health plans that do not meet minimum requirements under Obamacare was seen by some as an effort to protect Democrats from having to explain a new wave of policy cancellations during the final days of the fall campaign.
Obama has promised to help Democratic candidates any way he can, but told Senate Democrats last month that he would not be offended if those in conservative states do not want his help.
The president has acknowledged the difficulty of getting Democrats to vote in November. The electorate at midterm is typically smaller, older and whiter than in presidential election years, factors that favor Republicans.
That was the case in 2010, when the rise of the Tea Party movement carried dozens of Republicans to victory and sent a new generation of compromise-resistant conservatives to Washington.
"Too often, when there's not a presidential election we don't think it's sexy, we don't think it's interesting," Obama said this week at a Democratic National Committee dinner in Boston. "Because the electorate has changed, we get walloped. It's happened before and it could happen again if we do not fight on behalf of the things we care about."
RETIREMENTS HURT DEMOCRATS
Democrats have faced an uphill battle in Senate races from the start of the political cycle. Of the 35 Senate seats up for election, 21 are held by Democrats and 14 by Republicans, so Democrats have more seats to defend.
Beyond that, those Democrats include Mark Begich of Alaska, Mark Pryor of Arkansas, Mary Landrieu of Louisiana and Kay Hagan in North Carolina, who represent conservative states where Obama and Obamacare are particularly unpopular.
The top challengers to all four have raised significant campaign cash, and outside advocacy groups such as Americans for Prosperity, funded by billionaire brothers Charles and David Koch, already have spent millions of dollars on ads attacking the senators for backing Obamacare.
Republican candidates are heavy favorites to capture the seats of retiring Democrats Jay Rockefeller in West Virginia and Tim Johnson in South Dakota, two other states in which Obama's ratings are poor.
In Montana, Democrat John Walsh recently was appointed to fill the Senate seat vacated by Max Baucus, the new U.S. ambassador to China. Walsh is up for election in November and is running far behind Republican Steve Daines in early polling.
Democrats also could be stung by the retirement of Michigan Senator Carl Levin, which has put that state in play. Democratic Representative Gary Peters and Republican Terri Lynn Land, a former Michigan secretary of state, are now in a tight battle.
In Colorado, what had looked like a smooth path to reelection for Democratic Senator Mark Udall got much tougher last week when Republican Representative Cory Gardner announced he would take on Udall.
In Iowa, Democratic Senator Tom Harkin's retirement has given Republicans hope of picking up that seat. Representative Bruce Braley will be the Democratic nominee; the state's Republican establishment appears to be lining up behind state Senator Joni Ernst in a crowded primary field.
In another boost to Republican efforts, former GOP National Committee chairman Ed Gillespie jumped into the race against Virginia Democratic Senator Mark Warner, a former governor.
Gillespie is a long shot to defeat Warner, who is perhaps Virginia's most popular politician and has been endorsed by a former rival, retired Republican senator John Warner. But Gillespie's presence and fundraising prowess mean that Mark Warner's reelection might not be as easy as it once seemed.
Jennifer Duffy, a Senate analyst at the nonpartisan Cook Political Report, put Republican chances of a Senate takeover at 40 percent but said that could jump past 50 percent by November.
"The Republicans are competitive in places I didn't think they would be, but they still have some challenges," she said, citing the potential for divisive Republican primaries in Georgia, North Carolina and Iowa that could leave the party with weakened, ultraconservative candidates who might have difficulty winning.
In Georgia, Nunn could face either Phil Gingrey or Paul Broun, Tea Party favorites in the House with a history of inflammatory comments on the campaign trail.
Democrats are hoping for a repeat of 2010 and 2012, when Tea Party candidates won Republican primaries but blew winnable races by committing gaffes that helped Democrats paint the entire party as outside the nation's political mainstream.
"One thing Democrats have going for them is the Republicans' continued ability to put their own foot in their mouth by making one provocative statement after the other," said Jim Manley, a former aide to Senate Democratic leader Harry Reid.
"As folks step toward the voting booth, they are going to think long and hard about giving control of the Senate to a bunch of Tea Party types," Manley said.
Some Republicans say the party has learned from those mistakes. They note that in Colorado, Gardner's entry into the race led two other prominent Republicans to bow out, a sign that party officials' effort to avoid debilitating primaries might be gaining ground.
"I'm not seeing the problem with primaries materialize the way it did in previous cycles," said Brian Walsh, a former aide at the National Republican Senatorial Committee. "Primaries are only a problem when you nominate someone who can't win in November."