ST. LOUIS — Rep. Todd Akin vowed to fight on in his embattled Senate campaign, but a significant deadline loomed Tuesday that was bound to intensify pressure on the Missouri congressman to abandon the race over his comments that women's bodies can prevent pregnancies in cases of "legitimate rape."

Akin has been frantically trying to salvage his once-promising bid against incumbent Democrat Claire McCaskill in a race long targeted by the GOP as crucial to regaining control of the Senate. But ominous signs were mounting against the six-term legislator from suburban St. Louis, most notably the apparent loss of millions of dollars in campaign advertising money.

Early Tuesday Akin posted an apology video online, but made no mention of the race. He went on two conservative radio shows Monday, pledging to keep the campaign alive, even as some people in his own party urged him to step aside.