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Barack Obama stopped by a fundraiser for Doug Applegate, who is challenging Darrell Issa

The President went on a lengthy rant about Issa and GOP presidential nominee Donald Trump

La Jolla, California CNN  — 

President Barack Obama directed harsh criticism at Rep. Darrell Issa at a fundraiser Sunday in La Jolla, California, claiming the former House Oversight Committee chairman’s “primary contribution to the US Congress has been to obstruct and to waste taxpayer dollars on trumped up investigations that have led nowhere.”

Issa hit back at Obama, accusing the President of failing to take accountability “for the serious scandals that happened under his watch,” in a statement emailed to CNN Monday morning.

“I’m disappointed but not surprised that the president, in a political speech, continues to deny accountability for the serious scandals that happened under his watch where Americans died overseas and veterans have died here at home,” Issa said. “You’d be hard pressed to find anyone who thinks I’ve done too much to hold Washington accountable. I’ve worked with the administration on good legislation where it was possible, and called out wrongdoing wherever I saw it, and will continue to do so.”

Issa later told Fox News: “He’s making a big deal over something that I’m a little surprised that he’s punching down, but he is.”

Obama lashed out at Issa, who after years of challenging the President, is now touting his cooperation with the White House in a campaign mailer featuring an Obama photo. The Democratic candidate challenging Issa for his Southern California district – Doug Applegate – was in attendance at the $10,000-a-plate-and-up fundraiser.

“This is now a guy who because (Donald) Trump’s poll numbers are bad has sent of brochures with my picture on them touting his cooperation on issues with me,” Obama said. “That is the definition of chutzpah. Here’s a guy who called my administration perhaps the most corrupt in history.”

Obama said, “Beyond these interpersonal conversations, this is not somebody who is serious about working on problems.”

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Obama framed the Republican Party as being in lock step with the GOP nominee, saying, “It is absolutely vital we do everything we can to maximize turnout, maximize enthusiasm, reject Trump but also reject the climate that results in Donald Trump getting the nomination.”

“That starts in House of Representatives. The things you’re hearing Trump say, they’re said on floor of the House all the time. The Freedom Caucus in the House of Representatives are repeatedly promoting crazy conspiracy theories and demonizing opponents,” Obama said.

Repeating a thought from his stump speech earlier, Obama said Trump is only claiming credit for a longstanding Republican mindset.

“Donald Trump didn’t build that,” he said. “He just slapped his name on it and took credit for it.”

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The President said Issa had always been friendly to him – during the annual White House Christmas party. Obama said some GOP lawmakers tell him they’re “praying for you” during the holiday party photo-line.

“I don’t question the sincerity they are praying for me,” Obama said, before mimicking their prayer: “Please change this man from the socialist Muslim.”

“I’m sure it’s more sincere than that,” he conceded.

CNN’s Deena Zaru contributed to this report.