Rep. Joe Sestak's (D-PA) primary challenge to incumbent Sen. Arlen Specter just got a lot tougher.

By a 229-72 margin, the Pennsylvania Democratic State Committee voted Saturday to endorse Specter, who switched parties last April, in this year's Senate election. The margin easily surpassed the two-thirds majority required for a candidate to win the state party's official endorsement.

“I’m very proud to have been received to the party of my roots, very proud to be a Democrat, very proud to have a record of supporting the values of the Democratic Party as an independent voice in the senate for 30 years,” Specter said in his acceptance speech, according to PoliticsPA.com's Alex Roarty.

Specter, who already leads Sestak by more than 20 points in the most recent polls of the primary, spent most of his speech discussing former Republican Congressman Pat Toomey, the GOP's expected nominee, in the general election. In his last re-election bid in 2004, Specter defeated Toomey by 1.4% in the Republican primary. But in polling of this year's race, Specter trails Toomey by anywhere from 8-14 points.

“I can take Toomey on,” Specter said. “I’ve beaten him before.”

First, however, he'll have to hold off Sestak in the primary. And despite this defeat, Sestak said he isn't going anywhere. He called the state party's endorsement of Specter "just another deal" cut by politicians who don't understand that voters are tired of politics as usual.

“It’s going to be a great fight,” Sestak said of the ongoing primary battle.

But Sestak is running out of time and support. Even before yesterday's vote, the state party's chairman suggested that Sestak should drop out of the race. With a Specter-Toomey race likely to be one of this year's nastiest and costliest Senate elections, the party leadership is no doubt not happy to have a contested primary that will drain donors' resources and possibly divide the electorate.

Pennsylvania's primary election is on May 18.