As recently as February, Republicans were feeling confident about their chances of taking over the Senate in Tuesday's election. Nearly two dozen Democratic seats were up for grabs, and Republicans needed just four to secure a majority.

But eight months later, those takeover plans have all but unraveled. Even the most optimistic projections suggest the GOP is unlikely to defeat enough Democrats -- or hold on to enough of their own contested seats -- to take control of the chamber in this election.

"It's not impossible, but I don't think it's likely," Jennifer Duffy, who analyzes Senate races for the Cook Political Report, told The Washington Examiner.

Republican hopes began to fade in late February, when Sen. Olympia Snowe, a popular Maine Republican, announced her retirement. With no viable Republican replacement waiting in the wings, former Gov. Angus King, an independent, jumped in and is not only poised to win, but will probably vote with Democrats once he does.

The GOP also faced difficulties in Massachusetts once Democrat Elizabeth Warren entered the race against incumbent Republican Scott Brown. The contest quickly closed, and most polls give Warren a slight lead in the heavily Democratic state.

Adding to Republicans' woes is a North Dakota race in which the Democratic candidate proved so popular that the contest moved from the Republican win column to tossup. Then there were the setbacks in Indiana and Missouri, where Republicans undercut their own support with controversial comments about rape victims and abortion.

Duffy is now predicting Republicans will pick up no more than three seats, if any, leaving them one vote shy of the majority. In that scenario, Republicans' only hope would be that they also captured the White House so that a Republican vice president, Paul Ryan, could break ties in the Senate.

"I have a scenario where Republicans get four seats, but I just don't think it's likely," Duffy said. "I also have a scenario where the Democrats pick up one seat, but that is not likely."

Among the nail-biter Senate races to watch on Tuesday are:

» Montana: Incumbent Democratic Sen. Jon Tester is deadlocked with his Republican challenger, Rep. Denny Rehberg, who as the state's sole member of the House has statewide name recognition and a political organization comparable to Tester's.

» North Dakota: Voters found Democrat Heidi Heitkamp, a former state attorney general, so likable that the race against Republican Rick Berg moved from a sure Republican win to tossup.

» Virginia: Former Gov. Tim Kaine, a Democrat, and former Gov. George Allen, a Republican, have been virtually deadlocked from the start of this race for a seat being vacated by retiring Sen. Jim Webb, a Democrat who took the seat away from Allen six years ago. Late polls show Kaine pulling ahead.

» Wisconsin: Rep. Tammy Baldwin, a Democrat, is tied with former Republican Gov. Tommy Thompson, who served as secretary of health and human services under President George W. Bush, in one of the most bruising Senate races in the country.

» Indiana: Republican Richard Mourdock may have blown a significant lead in the race against Democratic Rep. Joe Donnelly after suggesting that a pregnancy resulting from rape is still "something that God intended to happen." Polls show the two deadlocked.