Virginia Republicans have announced a slate of three debates for the party’s U.S. Senate candidates, giving former governor George Allen’s foes some high-profile opportunities to derail his bid.

Allen is considered the clear frontrunner for the Republican nod in the race to succeed retiring Sen. James Webb (D). Fellow former governor Timothy M. Kaine is the expected Democratic nominee.

But Allen first has to get through the June 12 primary, in which he will face Bishop Earl Jackson, Del. Robert G. Marshall (Prince William), Hampton Roads lawyer David McCormick and former Virginia Tea Party Patriots head Jamie Radtke. All candidates on the primary ballot will be invited to the debates, slated for April 28 in Roanoke, May 11 in the Hampton Roads region and May 25 in Northern Virginia.

The exact locations and details of the debates will be released at a later date.

When the primary contest began Radtke was widely seen as Allen’s most formidable foe, because of her tea party ties. But she has struggled to raise money and so far there is little evidence she is making inroads against Allen. Marshall, meanwhile, only entered the race in mid-January, so he will have significant work to do to become a real threat to the frontrunner.