Donald Trump promises to attack Obama 'just like I hit Bill Clinton'

Donald Trump is preparing for a high-stakes rhetorical battle with President Barack Obama.

During a Wednesday-night rally in California, the presumptive Republican presidential nominee promised that when Obama begins seriously campaigning against Trump, he wouldn't take the criticism lying down.

"This is a president who doesn't have a clue," Trump said.

"He's going to start campaigning. Well if he campaigns, that means I'm allowed to hit him just like I hit Bill Clinton, I guess," he added.

As he began to broadly criticize Obama for allegedly not taking a more skeptical stance with US trade partners, the real-estate mogul was interrupted by a protester. Trump didn't linger on the subject, but a virtual back and forth Wednesday served as a preview of that battle throughout the summer and fall.

Despite the occasional jab at Trump, the president has largely stayed out of the fray, partially because of his promise to stay neutral in the Democratic presidential primary. But CNN reported on Thursday that the president will "explode onto the scene" once the Democratic primary concludes.

Trump's comments on Thursday came as Obama hinted at the tougher rhetoric he'll roll out once the general election begins in earnest.

During a Wednesday speech in Indiana, Obama methodically laid into Trump's proposals. He knocked the presumptive nominee's promise to eliminate the Wall Street financial industry regulations in the 2010 Dodd-Frank law, as well as Trump's rhetorical broadsides against immigrants living in the US without permission.

"If we turn against each other based on divisions of race or religion, if we fall for a bunch of 'okey-doke,' just because it sounds funny or the tweets are provocative, then we're not going to build on the progress we started," Obama said. "If we get cynical and just vote our fears, or if we don't vote at all, we won't build on the progress that we started."