Amid the uproar over Rep. Todd Akin’s comment on “legitimate rape,” one question has risen to the top: Did the Missouri Senate candidate just take his party one step away from taking over the US Senate?

Congressman Akin is now damaged in his quest to beat the most vulnerable Democrat in the Senate, Claire McCaskill, and his party knows it. Several Republican senators have called on him to drop out of the race. The senator in charge of the GOP’s Senate election effort, John Cornyn of Texas, said in a statement that Akin should take 24 hours and “carefully consider what is best for him, his family, the Republican Party, and the values that he cares about and has fought for throughout his career in public service."

The Cornyn statement suggested that Akin should quit the race, and raised doubts over whether the National Republican Senatorial Committee will invest money in the race if he remains a candidate.

In a radio interview Monday afternoon, Akin dug in his heels.

“To quote my friend John Paul Jones, I’ve not yet begun to fight,” Akin said on Mike Huckabee’s radio show.

Akin is reportedly being encouraged to stay in the race by his wife, who is a close adviser, and his son, who is running his Senate campaign.

Akin has also received statements of support from two prominent anti-abortion leaders – Tony Perkins, head of the Family Research Council, and Marjorie Dannenfelser, head of the Susan B. Anthony List. This opposing view raises the specter of a division among Republicans on the eve of their convention over the place of the abortion issue in the campaign. Many Republican leaders want to keep the campaign focused on the economy, President Obama’s weak spot, and away from divisive social issues.

The furor over Akin began on Sunday, when he asserted in a TV interview that pregnancy from rape is “really rare.” He was explaining his opposition to abortion with no exceptions.

“If it’s a legitimate rape, the female body has ways to try to shut that whole thing down,” Akin said on KTVI-TV in St. Louis. Later on Sunday, Akin said he “misspoke” but stood by his absolute position on abortion.

Akin won his party’s primary on Aug. 7, and has every right to stay in the race. It’s too soon to say how Akin’s comment will affect his challenge to Senator McCaskill, seen as one of the most endangered Democrats in the Senate, especially after the flap over her use of taxpayer money to pay for senatorial use of her private plane. Before Akin’s comment, he led McCaskill by an average of five percentage points.

Now, with Akin still running, McCaskill likely has a better shot at holding onto her job than she did before Sunday, and if she goes on to win, it’s likely she will owe her victory to Akin’s comment on rape.

The race for partisan control of the Senate, in fact, could hinge on this one race. The Republicans came into the 2012 cycle with the playing field tilted in their favor: The Democrats are defending 23 seats while the Republicans are defending only 10. And with a current 53-to-47 Democratic majority, all the GOP needs is a net gain of four seats to take over – or three, if Mitt Romney wins the presidency, since Vice President Paul Ryan would break any tie votes.

The nonpartisan Cook Political Report lists seven Democratic-held seats and three Republican-held seats as tossups. In two of the three Republican-held seats, the challengers have an excellent chance at winning: In Massachusetts, Democrat Elizabeth Warren can beat Sen. Scott Brown (R), who, despite his popularity, is playing on Democratic turf to hold onto the late Sen. Edward Kennedy’s old seat. In Maine, the retirement of Sen. Olympia Snowe (R) has opened a path for popular independent former Gov. Angus King, who hasn’t said which party he would caucus with, but it’s expected to be Democrats.

The third tossup race for a Republican-held seat, Nevada, pits Sen. Dean Heller against Rep. Shelley Berkley. But Congresswoman Berkley faces an ethics investigation, which damages her chances.

If Ms. Warren and Mr. King win their races, that raises the bar for the Republicans to take over five or six other seats. McCaskill’s is one they were counting on. In Nebraska, the seat currently held by retiring Sen. Ben Nelson (D) is a likely Republican takeover. In Wisconsin, moderate former Gov. Tommy Thompson’s primary victory last week positions the Republicans well to take over the seat of retiring Sen. Herb Kohl.

But the remaining Democratic-held tossup seats are harder to call. In Virginia, the race between two former governors – Tim Kaine (D) and George Allen (R) – is a dead heat. Also close is North Dakota, where a strong Democratic recruit – former state Attorney General Heidi Heitkamp – has made the race competitive against freshman Rep. Rick Berg, in a solidly Republican state.

In Democratic-leaning New Mexico, the race for the seat of retiring Democratic Sen. Jeff Bingaman pits Rep. Martin Heinrich (D) against former Rep. Heather Wilson (R). That’s another close one. Hawaii’s open Senate seat, currently held by retiring Sen. Daniel Akaka, should be easy for the Democrat – Rep. Mazie Hirono – in President Obama’s native state, but the Republicans’ recruitment of popular former Gov. Linda Lingle makes this race competitive.

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The final tossup seat is in Montana, currently held by Sen. Jon Tester (D). He’s being challenged by Rep. Denny Rehberg (R) in a race Cook Political Report says is likely to stay within the margin of error all the way to November.

If the Democrats win the Maine and Massachusetts seats, and hold onto the Hawaii, New Mexico, and Virginia seats (all states where President Obama is ahead) but lose the races in Wisconsin, Montana, Nevada, and North Dakota, then Missouri becomes the Republicans’ 50th seat. There are lots of other ways for the Republicans to get to 50 – or 51 – but by making Missouri more difficult, Akin has made a GOP Senate takeover a steeper climb.