If you still have doubts about whether Todd Akin is staying in the race for the U.S. Senate, you probably believe the moon is made of cheese.

At a St. Louis news conference, Akin repeated -- for maybe the 100th time today -- his assertion that he's sticking it out against Democratic incumbent Claire McCaskill.

"I have one purpose going into November, and that's replacing Claire McCaskill," the six-term congressman said.

The announcement came on the final day Akin could withdraw. If he should back out between now and election day, his name will still appear on the ballot.

Under fire for his comments about rape victims, Akin said the decision to pick him as the GOP nominee was made by the voters. He said he wouldn't violate their trust.

Akin surrounded himself with friends and supporters as he launched a statewide bus tour that begins today in St. Louis and brings him to Kansas City on Friday morning.

Billed as a news conference, Akin nonetheless declined to take questions at the end as is customary.

During his brief remarks, Akin criticized McCaskill for voting for the new federal health care law, which he said, 71 percent of Missourians opposed in a statewide vote. He said he received an "A" grade from the National Rifle Association while McCaskill got an "F."

And, he said, McCaskill has voted to raise 50 taxes. "I don't vote to raise our taxes," he said. "It's a clear choice."

Akin said Missourians have told him that they know that he can't be bought.

"A lot of people in politics specialize in asking this question: Can we win?" Akin said. "But there's another question that's more fundamental. That is, what's the right thing to do?

"There is an amazing correlation. When you do the right thing, you win anyway."