WASHINGTON (AFP) ― Republicans appear increasingly likely to win back the U.S. Senate in Nov. 4 mid-term elections, a move that would heap misery on President Barack Obama in his final two years in office.

The more conservative of the main American parties already controls the House of Representatives, and no one seriously predicts Democrats will retake it this year.

Republicans are capitalizing on stubbornly persistent frustration with Obama and his policies, particularly in battleground states Democrats must successfully defend if they want to hold the Senate.

Despite polls showing Democratic gains in some rollercoaster races, the math favors Republicans in their bid to win the six net seats they need to control the Senate.

“It’s not going to be a wave election, but it will bring a majority for the Republicans,” predicted American University professor James Thurber, who founded and directs the school’s Center for Congressional and Presidential Studies.

Forecast models by FiveThirtyEight blog and The New York Times say Republicans are between 62 percent and 64 percent favorites to seize the Senate majority. The Washington Post’s Election Lab puts Republican chances at 91 percent.

In one of several signs the GOP is tightening its election grip, the University of Virginia’s Center for Politics on Thursday shifted the key Arkansas Senate race from “leans Republican” to “likely Republican.”

“Republicans are hopeful that they’ve put this one away, and the trend line for Democrats is not good,” UVA wrote about Arkansas in its “Crystal Ball” report.

What would a full Republican takeover of Congress mean for the Obama administration? More gridlock and polarization, according to Thurber.

“It will be even worse with a Republican majority, and very little will get done on Obama’s legislative agenda,” which includes immigration reform, he added.

Republicans would likely take steps to dismantle or at least stop funding Obamacare, the president’s landmark health care reform law.

However, Democrats are not admitting defeat just yet.

Incumbents are holding their ground in New Hampshire, as well as in North Carolina, where a flood of money from outside groups is pushing the cost of that single Senate race to a record $100 million.

Complicating the election map, Republicans are vulnerable in traditionally deep red states Kansas and Georgia, both of which are too close to call.

Popular Kansas independent Greg Orman is neck and neck against veteran Senate Republican Pat Roberts, and has injected drama into the national picture by saying that if he won he would caucus with whatever party wins the majority.

Reflecting the fluid nature of races in the final weeks, Democratic groups pulled funding for Kentucky Senate candidate Allison Lundergan Grimes, only to acknowledge they are going back up with campaign ads there following her better-than-expected polling against five-term incumbent Republican Senator Mitch McConnell.

Republicans have had various degrees of success in tarring their rivals as rubber stamps for the president.

“In these finals days, the decision Americans face is becoming even clearer: a vote for a Democrat is a vote for the Obama agenda,” Republican National Committee chairman Reince Priebus said Thursday.

But Democrats like Alaska Senator Mark Begich reject the accusation they are in Obama’s back pocket.

“The president’s not relevant. He’s gone in two years,” Begich told the Washington Examiner.

Overall, Democrats maintain some advantages in 2014.

They poll better than Republicans on traits like honesty and willingness to compromise.

And Republican favorability among voters is 39 percent against 55 percent unfavorable, while Democrats fare better, at 47 percent against 48 percent, according to Pew Research.

With control of Congress at stake, Democrats have called in two political superstars ― former president Bill Clinton and potential 2016 frontrunner Hillary Clinton ― to sway undecided voters.

Both have lent their political celebrity at several Democrats’ campaign stops, but it is unclear if their support will move the needle.

“The Clinton magic is not enough in my opinion,” Thurber said.

When the sun rises on Nov. 5, there is a good chance the fate of the Senate could still be undecided.

Louisiana and Georgia, where several Senate candidates are on the ballot, require runoffs if no candidate receives more than 50 percent of the vote.

With neither Senator Mary Landrieu nor her main Republican rival Bill Cassidy close to that threshold in polling, a Dec. 6 runoff in Louisiana is a foregone conclusion, experts say.

A January 6 runoff in Georgia would mean control of the Senate might not be decided for a full two months after election day.