Donald Trump has questioned American intelligence about foreign meddling in the US election, claiming Russia was not the only country that might have interfered.
"Nobody really knows for sure," the president said, on the eve of his first meeting with Russian leader Vladimir Putin.
As US investigations into Russian meddling move ahead, Mr Trump is under intense scrutiny for how he handles his first face-to-face session with Mr Putin.
US intelligence officials say the unpredictable Russian president ordered interference in the election that took Mr Trump to the White House.
The pair plan to sit down on Friday in Hamburg, Germany, on the sidelines of an international summit.
Loath to cast a shadow on his election victory, Mr Trump has avoided firmly blaming Moscow for campaign hacking in the past, and on Thursday, he was similarly elusive.
He argued variously that it could have been Russia, probably was Russia and indeed was Russia, while insisting it could have been other countries, too, adding: "I won't be specific."
"A lot of people interfere. It's been happening for a long time," Mr Trump said. He did not say whether he planned to discuss the issue with Mr Putin.
The president sought to redirect any scrutiny toward his predecessor, Barack Obama, accusing him of allowing Moscow to meddle on his watch.
Though the Obama administration warned Russia publicly and privately before Election Day to stop interfering, questions have since been raised about whether he acted firmly enough to stop the threat.
"They say he choked. Well, I don't think he choked," Mr Trump said. "I think he thought Hillary Clinton was going to win the election, and he said, 'Let's not do anything about it'."
Mr Trump said the CIA had informed Mr Obama about the hacking months before the election but added that "mistakes have been made".