Washington — President Donald Trump heads into his meeting with Russian President Vladimir Putin with one question looming large: how much is he willing to confront the man whose meddling in the 2016 election may have helped him win?

The encounter scheduled for the sidelines of next week’s G-20 summit in Germany comes amid a widening federal investigation into possible collusion between Trump associates and the Russian government. Trump last week gave a rare explicit acknowledgment of the Kremlin-directed effort to disrupt the U.S. presidential campaign.

National Security Adviser H.R. McMaster told reporters on Thursday there was no set agenda for the meeting, and he didn’t know whether the president planned to raise the issue of electoral interference.

But for Trump, who remains a foreign policy novice, the encounter could prove a defining moment in his presidency. Five months after becoming commander-in-chief, he’s now responsible for confronting foreign efforts to undermine national security.

While Trump referenced Russia’s meddling in the U.S. election in a tweet on June 23, he did so by blaming his predecessor in a series of tweets for not having done more to stop the interference.

During next week’s Group of 20 meeting in Germany, Trump will be under intense pressure to demonstrate that he’s not the Putin “puppet” Democratic opponent Hillary Clinton labeled him during the campaign. Not only will American voters and foreign leaders be watching, but so will a special counsel now examining whether Trump tried to impede the Russia investigation.