Russian President Vladimir Putin lobbied U.S. President Donald Trump during their meeting to extend various nuclear treaties and pursue weapons limits in Helsinki last month, according to a leaked document described by Politico.

News analyst Charlie Sennott called the contents of the document “pretty serious stuff that was on the table” during an appearance on Boston Public Radio today.

“Putin was in there lobbying Trump on arms control, talking with him about what kinds of things he wants to put forward for his agenda,” Sennott said. “This is what this leaked document is really revealing for the first time for us.”

Trump and Putin had a private meeting during their recent summit in Helsinki, which alarmed critics of Trump who worry about his cozy relationship to the Russian president.

Sennott said the fact that the men were discussing “controlling nuclear arms” and “prohibiting weapons in space” is evidence that Trump should not be left alone to talk to world leaders, because he might discuss agenda items with major diplomatic consequences.

“This is why it's a really bad idea to have this guy off on his own, talking to someone as knowledgeable as Putin, with as clear an agenda as he wants to put forward,” said Sennott.

Charlie Sennott is a news analyst here at WGBH, where he also heads up The GroundTruth project.