Trump needles debating Democrats via Twitter

Republican presidential frontrunner Donald Trump was not about to let Democrats steal the limelight in their first 2016 debate, offering his own running commentary of proceedings and their electoral chances.

The carefully coiffed real estate mogul needled his possible general election adversaries on Twitter on Tuesday, even before they took to the lecterns.

Trump said he felt sorry for three candidates -- former Maryland governor Martin O'Malley, ex-senator Jim Webb and former Rhode Island governor Lincoln Chafee -- polling at less than one percent.

"Maybe a star will be born (unlikely)," he said.

As the debate kicked off, he was no less scathing.

"Can anyone imagine Chafee as president?" he asked. "No way."

"O'Malley, as former Mayor of Baltimore, has very little chance."

Trump also trained fire on Clinton, hitting the former Secretary of State for backing a vast trans-Pacific trade deal she now opposes.

"The trade deal is a disaster, she was always for it!" Trump tweeted.

And he returned to his common refrain that only he can stand up for America on the international stage.

"Putin is not feeling too nervous or scared," he said.