A day before his first face-to-face meeting with Russian leader Vladimir Putin, President Trump agreed that Moscow meddled in the 2016 election but also claimed “other people” could have interfered – “nobody really knows for sure.”

“I think it was Russia and I think it could have been other people in other countries,” Trump said during a joint press conference with Polish President Andrzej Duda, before throwing doubt on his own comments. “It could have been a lot of people interfered.”

Trump said he couldn’t be specific, but that other countries also get involved in elections and have been doing so for a “long period of time.”

“I think it was Russia but I think it was probably other people and or countries, and I see nothing wrong with that statement,” he said when pressed on Russian involvement.

“Nobody really knows,” he added. “Nobody really knows for sure.”

The US intelligence community has concluded that Russia interfered in the election at the direction of Putin. It’s now the subject of a number of congressional investigations, as well as the FBI and special counsel Robert Mueller.

Trump also blamed former President Obama for not taking a more active role to stop Russian hacking in the election after the US intelligence community informed him of the meddling last summer.

“They say he choked. Well, I don’t think he choked,” Trump said. “I think he thought Hillary Clinton was going to win the election, and he said, ‘Let’s not do anything about it.'”

Members of the Obama administration said they were reluctant to go public with the information out of fear they would themselves be interfering in the election.

They opened an investigation into Russia’s involvement and reached out to state election boards to offer help to secure their voter systems.

Trump said Obama should have done more.

“And he said, lets not do anything about it. Had he thought the other way, he would have done something about it,” he continued. “So that’s the real question is why did he do nothing from August all the way to November and why did he do nothing.”

Trump is expected to meet with Putin on the sidelines of the G-20 summit on Friday in Hamburg, Germany.

The Kremlin and the White House haven’t given details of what’s on the agenda, including whether Trump will bring us the Kremlin’s involvement in the presidential election.

Other topics include global terrorism, the civil war in Syria and Russia’s annexing of Ukraine.