Trump, Putin shake hands ahead of high-stakes meeting at G-20

Trump is meeting with the Russian president for the first time.

The White House has said no agenda has been set for the discussion, but topics that are likely to come up include Syria and Ukraine. What's unclear is if Trump will reprimand Russia for its alleged hacking in the 2016 U.S. election and European elections.

Yesterday, in a press conference on foreign soil, President Trump questioned the U.S. intelligence community's findings that Russia meddled in the 2016 election and insisted "nobody really knows."

Trump also was tough on former President Obama, saying his predecessor "choked" and "did nothing" when he found out in August 2016 about Russia's cyber operation to disrupt the 2016 election.

ABC News' Marcus Wilford and Alexander Mallin contributed to this report.