Mark Pryor Going on the Air #ARSEN

Pryor is running advertisements for his re-election bid. (Chris Maddaloni/CQ Roll Call File Photo)

Sen. Mark Pryor, D-Ark., will launch a television ad campaign on Friday — 17 months before this cycle's most vulnerable incumbent faces voters in the general election.

"It’s an ad in response to the attacks we’re getting on both sides," Pryor campaign manager Jeff Weaver said. "These outside groups are trying to affect the election. So we’ve produced an ad."

Pryor has been hit on the air by the conservative groups Club for Growth and Senate Conservatives Fund for his ties to President Barack Obama. New York Mayor Michael Bloomberg's super PAC, Mayors Against Illegal Guns, just launched a $350,000 ad buy hitting Pryor for his vote against expanded background checks.

(See also in Roll Call: Pryor Can't Escape 2010 Comparison)

Weaver declined to disclose the size of the ad buy or how long the ad will air. Politico, which first reported the buy, reported that the campaign has so far placed a $30,000 buy for a week-long flight.

Pryor had $3.4 million in cash on hand as of the end of March. He is still awaiting a Republican challenger. At this point, freshman Rep. Tom Cotton appears to be Pryor's most likely opponent, though he has not indicated which way he is leaning.

Rothenberg Political Report/Roll Call rates this race as Pure Tossup.