Veteran US senator Specter loses primary

Veteran US Senator Arlen Specter, who quit the Republican Party to become a Democrat a year ago, has lost his bid for a new term as voters backed his usptart challenger.

President Barack Obama's endorsement and backing from the state and national party establishment failed to pull Specter over Representative Joe Sestak, a retired vice admiral with appeal among core Democratic supporters.

With most official returns in, US media and the Democratic Party projected Sestak would beat Specter, a moderate lawmaker with 30 years of Senate experience.

"Joe Sestak has a compelling life story, and a powerful message of change," said Senator Robert Menendez, chair of the Democratic Senatorial Campaign Committee.

"He knows what is wrong with Washington, and if elected to the Senate, will shake up how business is done in the Capitol."

Party-switch unpopular

Sestak was all but certain to face Republican former representative Pat Toomey - who has led both Democrats in recent polls - in November elections to decide control of Congress.

Sestak's stunning come-from-behind victory - he was down double-digits in public opinion polls just months ago - came as US voters angry with the Washington status quo rebuked established candidates in a series of key races.

Specter also suffered among Democratic voters for his party-switching, which he had explicitly labeled as an attempt to save his faltering reelection bid, and his previous ties to former Republican president George W Bush.

Menendez said in his statement that he had "tremendous respect" for Specter, calling him "a loyal member of the Democratic caucus" and a key player in the achievements of the president's party since January 2009.

"With his support, Democrats passed landmark health care reform, a jobs package, and of course the Economic Recovery Act, which saved the nation from an economic abyss," he said, referring to a massive stimulus package.