Current and former US officials have sounded the alarm about President Donald Trump's upcoming summit with Russian President Vladimir Putin.

US officials expressed concern over how quickly Trump was willing to meet with Putin.

Over a dozen officials indicated "that there is no historical precedent for such a meeting.

Current and former US officials sounded the alarm about President Donald Trump's upcoming summit with Russian President Vladimir Putin.

"I'm afraid," a former State Department told The New Yorker in a story published on Friday. "Our guy here is like an amateur boxer going up against Muhammad Ali."

"There's no stopping him," a senior White House official reportedly told veteran journalist and New Yorker writer Susan Glasser in June. "He wants to have a meeting with Putin, so he's going to have a meeting with Putin."

Citing interviews with more than a dozen former senior officials who worked for Republican and Democratic presidents, Glasser indicated there is "no historical precedent for Trump's meeting with Putin."

This approach to diplomacy with Russia has confounded some foreign-policy experts, as it's happening despite the US intelligence community's conclusion that Russia meddled in the 2016 US presidential election, and accusations that Russia carried out a nerve-agent attack in the UK in March.

Trump's Singapore summit with North Korean leader Kim Jong Un in June was also met with early doubt, given the reclusive nation's pattern of behavior and Kim's mercurial nature. But Tom Graham, the National Security Council's former senior director for Russia, told The New Yorker that the US "had more time for planning," compared to Trump's upcoming meeting with Putin.

In preparation for the US-North Korea summit, Secretary of State Mike Pompeo twice flew to North Korea and US intelligence officials met with their North Korean counterparts on several occasions.

Based on media reports, preparations for the US-Russia summit appear to have been limited — aside from a group of Republican lawmakers visiting Russia during the week of Independence Day. National security adviser John Bolton reportedly flew to Moscow once.

President Donald Trump and Russian President Vladimir Putin at the APEC Summit in Vietnam in 2017. Jorge Silva/Reuters

That summit has also been overshadowed by the Justice Department's indictment of 12 Russian intelligence officers in connection with the hacking of several Democratic Party organizations and Hillary Clinton's presidential campaign in 2016. Russian intelligence officers tried to hack email accounts affiliated with Clinton's campaign by sending "spearphishing" emails to employees with links that contained malware.

In light of the indictment, both Democratic and Republican lawmakers, including the Arizona Sen. John McCain, called on Trump to cancel the Putin meeting.

"If President Trump is not prepared to hold Putin accountable, the summit in Helsinki should not move forward," McCain said in a statement on Friday.