Republican Pat Toomey has agreed to debate Rep. Joe Sestak (D-Pa.), setting up a potential Senate candidate showdown that would leave incumbent Sen. Arlen Specter on the sidelines.

In a letter sent to Sestak Monday, Toomey said he would welcome a joint forum focused on the economy and commended the Democrat for his interest in pursuing it.

Last week, Sestak’s campaign proposed a debate with Toomey after complaining about Specter’s refusal to debate in each of the state’s six media markets.

“Unfortunately, Sen. Specter has refused all but a one-hour debate in Philadelphia in May, and has already rejected invitations to participate in forums in Lancaster, Erie and another event in Philadelphia. I believe it would be a benefit to Pennsylvania voters for you to take Sen. Specter's place at one or all of these events, or at separate forums our campaigns could work together to develop,” wrote Sestak on Feb. 18th.

Seizing on the opportunity to double-team Specter, Toomey wrote back Monday that he could understand Sestak’s frustration.

“Like many politicians who have spent decades in Washington, Sen. Specter maintains a sense of entitlement to his office and he is unwilling to put his record and ideas to the test of open and honest debate,” wrote Toomey.

“If Senator Specter isn’t going to debate, we can have the same debate with Congressman Toomey that Senator Specter’s not going to,” Sestak spokesman Jonathan Dworkin told POLITICO.

But Specter’s campaign points out that the two Democrats have already debated once earlier this month at the state Democratic convention in Lancaster and that a May 1st Pennsylvania Broadcasters Association debate will air live on at least one station in each of the state’s television market in addition to a cable network.

“Sen. Specter has traditionally participated in one live, statewide TV debate during the primary,” said Specter spokesman Chris Nicholas, when asked why his candidate wasn’t agreeing to more.

He also accused Sestak of debate hypocrisy.