Akin is in a three-way primary race with John Brunner and Sarah Steelman vying for the Republican nomination in the Aug. 7 Missouri primary. The winner will face Sen. Claire McCaskillClaire Conner McCaskillSenate moderates hunt for compromise on family separation bill Election Countdown: Family separation policy may haunt GOP in November | Why Republican candidates are bracing for surprises | House Dems rake in record May haul | 'Dumpster fire' ad goes viral Hillicon Valley: Verizon, AT&T call off data partnerships after pressure | Tech speaks out against Trump family separation policy | T-Mobile, Sprint make case for B merger MORE (D-Mo.) in November.

Huckabee, a former Arkansas governor and Republican presidential candidate, could help rally Evangelical voters to Akin. In the ad, Huckabee calls him a "courageous conservative" and "a Bible-based Christian" who "supports traditional marriage, defends the unborn and voted to defund Planned Parenthood."

A spokesman for Brunner criticized Akin for failing to speak for himself in the ad.

"Congressman Akin's new television ad fails to answer any of the questions that Missouri voters have about his voting record while in Congress, specifically, why he voted four times to raise the nation's debt limit by over $3 trillion and why he has wasted billions of dollars on reckless earmark spending," Brunner campaign spokesman Todd Abrajano said in a statement released to media outlets. "We look forward to hearing what Congressman Akin has to say when he starts speaking for himself."

Brunner was ahead of his fellow Republican contenders, according to an internal poll released by his campaign late last month.

The Hill rates the race a "toss-up."