Sen. Lamar Alexander (R-Tenn.), left, and Senate Minority Leader Mitch McConnell (R-Ky.) at a news conference on Capitol Hill on Nov. 21, 2013. (Gary Cameron/Reuters)

Sen. Lamar Alexnader (R-Tenn.) raised more than $900,000 between April and June and has a hefty $3.4 million in his campaign account as he looks to fend off a tea party challenger in the Aug. 7 primary.

Alexander's campaign announced his total Wednesday morning. The second-quarter fundraising period ended Monday.

Alexander is one of two Republican senators with primaries coming up in August against conservative challengers. The other is Sen. Pat Roberts (Kan.). Both are favored to win.

The senator from Tennessee, a former presidential candidate, faces a slate of primary challengers. The biggest threat appears to be Joe Carr, a state legislator running to his right. Polls show that Alexander is not at serious risk of losing at this point.

Still, he's guarding his right flank. The senator is out with a new TV ad that shows him sparring with President Obama over the federal health-care law.

Carr had about $467,000 in the bank at the end of March.

No Republican senator has fallen in a primary this year.