Back at the White House on Tuesday, the president told reporters that he said he meant he does not see why Russia “wouldn’t” be responsible.
He also said he accepts the American intelligence community’s conclusion that Russia interfered in the election, but he denied that his campaign had colluded in the effort.
Mr Trump spoke a day after returning to the US to nearly universal condemnation of his performance at Russian President Vladimir Putin’s side in Helsinki.
Mr Putin said he wanted Mr Trump to win the race against Democrat Hillary Clinton.
In Helsinki, Mr Trump delivered no condemnation of Russia’s interference and refused to say he believes American intelligence agencies over Russia’s denials of meddling.