Washington (CNN) -- Instead giving in to fellow Republicans desperate for him to drop out of the Missouri Senate race, a defiant Todd Akin gathered conservative supporters and launched a campaign bus tour.
"I have one purpose going into November and that's replacing [Democratic Senator] Claire McCaskill," the congressman said to an applauding crowd in St. Louis on Tuesday, the last day state law permitted him to remove his name from the ballot.
"A number of people have asked me if I'm dropping out," said Akin, whose controversial comments on rape and pregnancy in August triggered a national uproar and turned him into a political pariah.
He added that this is "not my decision," but rather the decision of Republican voters who chose him this summer as their candidate against McCaskill in a race considered crucial for control of the Senate.
Senior Republican sources told CNN that they gave up on pushing Akin out of the contest some time ago after he refused to bow to pressure. The Republican Party chairman, GOP congressional leaders, Mitt Romney and Paul Ryan joined together to publicly call on him to step aside.
Ryan telephoned Akin to try to convince him to go.
"Probably the best thing for Todd to do, for his own campaign and for the country, is not to run," Ryan said at the time.
Republican Party leaders had counted on beating McCaskill, long considered one of the Senate's most endangered Democrats, but they have all but given up. They won't give Akin a dime, nor will leading outside groups with deep pockets like Crossroads GPS.
But Akin still has support from some high-profile conservatives like Newt Gingrich, who is helping to raise money.
The former House speaker campaigned with Akin on Monday and chastised the GOP establishment for abandoning him. Akin backers are also hoping to win support and money from Sen. Jim DeMint, R-South Carolina, who has a track record of helping the most conservative Senate candidates.
Akin advisers insist that polls show he is still competitive and that national Republicans will have egg on their faces when he proves them wrong by winning in November.
But national GOP strategists say they believe the only reason the race is close is because McCaskill has been waiting for the legal deadline for Akin to drop out to pass before going after him.
She agrees with national Republicans that Akin is the most beatable of any GOP candidate -- especially since his incendiary gaffe. McCaskill has been limiting her television ads to promoting herself instead of slamming her opponent.
Republican strategists who have written off the Missouri race admit it has put GOP chances for seizing the Senate majority at major risk.
A look the math helps explain why: Republicans currently hold 47 of 100 seats. To win outright control, they must pick up four seats that are held by Democrats, assuming they lose none themselves.
The most likely place for a GOP win is the open Democratic seat in Nebraska. Other states in the toss up column that Republican strategists say they're hoping to snatch include North Dakota, Wisconsin, Montana, Connecticut, Virginia and Ohio.
What makes the GOP road to the Senate majority even tougher is that polls show Republicans risk losing two seats: Scott Brown's in Massachusetts and the one left open in Maine by retiring Olympia Snowe.
If Republicans lose those seats, which GOP strategists tell CNN is quite possible, they admit they would have to sweep the toss-up races to take control of the chamber.
That's doable, GOP sources say, but very difficult.
It's a surprising struggle for Republicans, given that the majority of senators up for re-election are Democrats, and the national climate -- namely the weak economy -- has been bad for Democrats.
Republican strategists charged with winning enough seats to retake the Senate majority told CNN that one reason it has become more difficult than they expected is because Romney is struggling in the presidential race.
That's especially true, these sources said, in the presidential battlegrounds of Virginia, Ohio and Wisconsin where Romney has fallen behind President Barack Obama and, according to one GOP source, is "dragging Senate candidates down with him."