WASHINGTON (CNN) -- Even before a second Republican Senate candidate tripped over incendiary comments about rape, GOP leaders in Washington knew that their once promising chances of winning control of the Senate had diminished.
Whether Richard Mourdock of Indiana can move past his controversial remarks and stabilize his campaign remains to be seen. Either way, once confident Republicans across the country now face the nail-biting final days of campaigning and a highly uncertain outcome on Election Day.
That's a big change from two years ago when Republicans made major gains in the midterm election and had reason to believe they could take back the Senate this year. But, in fact, Democrats now appear well-positioned to retain their slim majority and with it the ability to influence much of the Washington agenda during the next two years whether President Barack Obama is re-elected or former Massachusetts Gov. Mitt Romney succeeds him.
Political operatives in each party caution that there are more toss-up races this year than in recent memory, so it's very hard to predict the outcome which they agree could be influenced heavily by the presidential ballot.
"We are cautiously optimistic that we'll keep the majority this year," said Matt Canter of the Democratic Senatorial Campaign Committee, which coordinates Democratic campaigns. He pointed to Democratic Senate candidates who are doing unexpectedly well in several red states, which is forcing Republicans to focus their energies and resources where they didn't expect to have to.
"Republicans are spending millions of dollars playing defense in five of the 10 Republican-held seats on the map," Canter said. "Pundits didn't predict that."
Republicans, who acknowledge they faced a number of setbacks, have been buoyed recently by the resurgence of Mitt Romney's presidential bid and are hopeful his momentum will carry over to Senate races. Romney recently cut ads for two GOP Senate candidates, which will test that theory.
"What the first (presidential) debate did was clarify the choice between the two visions of the parties and that helped us," said Rob Jesmer of the National Republican Senatorial Committee, which spearheads the GOP election effort.
Jesmer said that of the 10 to 12 races that are polling within the margin of error, Republicans believe they are actually ahead by a couple of points in most of them. The Republican senatorial committee and GOP super PACS plan to spend heavily in Indiana, Wisconsin, North Dakota, Montana, Nevada, Arizona, and Virginia between now and the election.
"The races are close and millions of dollars will be spent" in the coming days, Jesmer said. "So we have to run to the tape."
Two years ago, Republicans were upbeat about their prospects because they only needed four seats to win the chamber outright and just three if a Republican were to win the White House and a GOP vice president could break tie votes.
Republicans had the advantage of having to protect only 10 seats while Democrats had to defend 23, many in narrowly divided swing states. In addition, several veteran Democratic incumbents, mostly moderates, announced they would retire, making it potentially even easier for Republicans to win those seats. Republicans encountered their own problems, though.
A frustrated Sen. Olympia Snowe of Maine, who was considered a shoo-in for re-election, shocked her colleagues when she suddenly announced that she would leave the Senate, which she described as hopelessly partisan. In Missouri, the campaign of Rep. Todd Akin nearly collapsed after the Republican's comments about "legitimate rape" and his suggestion that women could biologically prevent pregnancy if they are raped. Until then, Republicans believed Akin would defeat Democratic Sen. Claire McCaskill, who polls showed was not very popular after just one term.
Now, Republicans are grappling with the controversy over Mourdock, the tea party-backed state treasurer. He had already riled the Republican establishment by defeating in the primary longtime moderate Sen. Richard Lugar, who otherwise likely would have won a seventh term. During a televised debate with his opponent, conservative Democratic Rep. Joe Donnelly, Mourdock defended his opposition to abortion even in the case of rape because, "I think even when life begins in that horrible situation of rape, that it is something God intended to happen."
Democrats pounced on his remarks and several key Republicans denounced them, too. Romney, who had just appeared in a TV ad for Mourdock, said he disagreed with the comment but didn't pull his endorsement.
Democrats, who this week pumped an additional $1.6 million into the race, say their internal polling shows Donnelly up by two points. However, Republicans say they are confident that the heavily GOP and pro-life voters in Indiana will rally behind Mourdock.
Strong Democratic candidates also have put several GOP seats into play.
In Arizona, former President George W. Bush's Surgeon General Richard Carmona, a Democrat who is Hispanic, is neck and neck with veteran GOP Rep. Jeff Flake. In Massachusetts, former Obama administration consumer advocate Elizabeth Warren appears to be slightly ahead of Sen. Scott Brown, the Republican who won the Senate seat that for decades belonged to Ted Kennedy. And in Nevada, many polls indicate Democratic Rep. Shelley Berkley narrowly trails Sen. Dean Heller, the Republican.
In three of the states where moderate Democratic incumbents retired this year and Republicans were early favorites to win, polls now show tight races. In Wisconsin, Democratic Rep. Tammy Baldwin is neck and neck with former GOP Gov. Tommy Thompson. In North Dakota, Democrat Heidi Heitkamp is slightly behind Republican Rep. Rick Berg and in New Mexico, Democratic Rep. Martin Heinrich is holding a small but steady lead of former Republican Rep. Heather Wilson.
But Republicans point to their own prospects, including seats they hope to pick up across the aisle.
At the top of their list is in Nebraska where Republican Deb Fischer has a solid lead over former Democratic Sen. Bob Kerrey and is likely to win the open Senate seat being vacated by Democrat Ben Nelson.
In Democratic-leaning Connecticut, Republican Linda McMahon, the former professional wrestling executive, hopes to win the seat of retiring Sen. Joe Lieberman, the independent who caucuses with Democrats. Her opponent is Democratic Rep. Chris Murphy, who has struggled to maintain a lead over McMahon. The race has been notably caustic with negative advertising flooding the airwaves. Democrats have had to spend heavily to shore up Murphy's campaign.
Polls are also very close in Montana where incumbent Democrat Jon Tester is locked in a slugfest with GOP Rep. Rick Berg and in Virginia where former Democratic Gov. Tim Kaine is trying to hold onto a Democratic seat over former Republican Sen. George Allen.
Democratic seats in Florida and Ohio are also in play although currently the Republican challengers appear to be behind.