Washington, Embattled US President Joe Biden's campaign released a new ad on Thursday, criticizing rival and former President Donald Trump for "siding with Putin" and calling him a "dictator's lapdog."

The ad, released to coincide with the final day of the high-profile NATO summit here this week, is part of a larger $50 million paid media buy for July, ahead of the presidential election. on November 5.

The announcement also comes as Biden, 81, faces the daunting task of reassuring fellow Democrats and voters about his fitness for office after a disastrous debate performance against Trump, 78.

The ad criticizes Trump for suggesting that Russia "do whatever it wants" to NATO members that don't meet defense spending targets, and warns that the presumptive GOP nominee is "a lapdog for a dictator who blame 'America First.'"

"Donald Trump is an unhinged would-be dictator. If re-elected, he will be Vladimir Putin's lapdog, giving him the green light to crush Europe and potentially spark World War III," Biden campaign spokeswoman Lauren Hitt said Thursday. , cited by CNN.

"Democracy and American security are in the November election, and President Biden is the only candidate in this race committed to protecting and promoting them at home and abroad," she said.

Congressional Democrats are concerned about Biden's chances of winning re-election, particularly in the wake of his disastrous CNN debate last month, and that having him at the top of the ticket could also hurt the party in the election.

Most Democrats have been reluctant to publicly call on Biden to step aside, but a growing number are saying so out loud, even after Biden went on the offensive this week to shore up support for a second term in the White House.

Biden wrote to congressional Democrats on Monday that he will continue his re-election bid despite growing concerns.

Meanwhile, Biden is scheduled to hold a closely watched news conference Thursday at the end of the NATO summit, marking another high-stakes moment to showcase his ability to answer questions in an improvised setting.