After face-to-face talks with Russian President Vladimir Putin, Mr Trump contradicted US intelligence agencies and said there had been no reason for Russia to meddle in the vote.
Mr Putin reiterated that Russia had never interfered in US affairs.
The two men held nearly two hours of closed-door talks in the Finnish capital Helsinki on Monday.
At a news conference after the summit, President Trump was asked if he believed his own intelligence agencies or the Russian president when it came to the allegations of meddling in the elections.
“President Putin says it’s not Russia. I don’t see any reason why it would be,” he replied.
US intelligence agencies concluded in 2016 that Russia was behind an effort to tip the scale of the US election against Hillary Clinton, with a state-authorised campaign of cyber attacks and fake news stories planted on social media.
In a strongly-worded statement, US House Speaker Paul Ryan said Mr Trump “must appreciate that Russia is not our ally”.
Of course, we don’t know what was accomplished in private yet, but the public outcome of Trump’s meeting with Putin left a lot to be desired.