Polling showed Akin trailing Brunner and Steelman in late July, but Akin expressed confidence that he was closing strong. He is the only leading Republican not to have run negative ads against his rivals.
In Wisconsin's Senate race, Thompson was ahead in the polls last month. Yet political newcomer Eric Hovde, a hedge fund manager, and former two-term Rep. Mark Neumann are hoping for a Cruz-like bounce before the Aug. 14 Republican primary. Hovde, who has the backing of FreedomWorks, has spent at least $4 million of his own money while portraying himself as the most fiscally conservative candidate.
But Neumann, who was third in the polls, may stand to benefit the most if there is a tea party surge. He has the backing of Sens. DeMint and Paul, as well the Club for Growth. The day after Cruz won in Texas, Neumann began airing a TV ad that touts him as "conservative before it was cool" — noting he was removed from a House subcommittee in 1995 for refusing to go along with Republican leadership.
The quest to be the most conservative has been central to many Republican primaries this year.
In Arizona's Aug. 28 primary for Senate, Palin has endorsed Rep. Jeff Flake, a longtime crusader against spending earmarks who is seeking to succeed retiring Sen. Jon Kyl. Flake also has the support of Kyl and Arizona Sen. John McCain.
Yet real estate mogul Wil Cardon, who casts himself as a tea party candidate, has lent his campaign more than $6 million while trying to position himself to the right of Flake. One Cardon television ad featured an altered photo that made it appear that Flake literally stood behind President Barack Obama — suggesting Flake's stance on immigration was the same as the Democratic president.
Unlike in the Texas contest, it's not so easy in Arizona, Wisconsin or Missouri to clearly distinguish the tea party favorite.
Analyzing the Missouri race, Akin conceded that despite his congressional tea party support, Palin's help for Steelman is "pulling some of our social conservatives, and Brunner is taking our economic conservatives.
"The question is how does that all break down? Akin asked. "I don't think anybody really knows."
Associated Press writer Scott Bauer in Madison, Wis., contributed to this report.