THE ALARMS over President Trump’s second meeting with Russian President Vladimir Putin at the Group of 20 summit are, in one way, overheated. Staying engaged with Russia and its leader, including through a spontaneous pull-aside at a closed dinner for world leaders, is not in itself a fault: At best, it might help alleviate mistrust and avoid miscalculation at a time of high tension. While it is possible to object to Mr. Trump’s impulsive style and tendency to bypass established channels, the problem is not so much that he sought out Mr. Putin for an informal chat. Rather, it is the deeply troubling and unresolved questions about his relationship with Russia, which mean that any such contact raises serious — and understandable — concerns.

“Engagement” is not a dirty word. Even in the worst days of the Cold War, in the shadow of the Cuban missile crisis and the 1983 war scare, the United States remained in close communication with the Soviet Union. A back channel often proved vital. During the tense days of autumn 1983, the National Security Council specialist on Soviet affairs, Jack F. Matlock Jr., met quietly in a cafeteria opposite the Old Executive Office Building with a Soviet journalist he had known, who revealed the dire situation in Moscow, including Soviet leaders’ deepening uncertainty about possible war with the United States. This was important information.

Talk isn’t bad; what’s key is the nature of the talk. To carefully calibrate messages to world leaders, presidents usually rely on an elaborate bureaucratic machine, including the interagency process and the National Security Council staff. Mr. Trump’s dinner chat showed once again his proclivity to act alone, and he undoubtedly created headaches. With no U.S. note-taker or interpreter, the U.S. national security structure was left without a record of the exchange, except for Mr. Trump’s memory. Mr. Putin will have a better record.

But the deeper problem is the epidemic of mistrust Mr. Trump has created about his ties to Russia, which sensationalizes contacts that might otherwise be unremarkable. The doubts began during the campaign with his failure to release his tax returns, which could show the origins of his income, and grew worse when Russia hacked the Democratic National Committee and the email account of Hillary Clinton’s campaign chairman. Mr. Trump refused to accept U.S. intelligence community warnings of Russian interference during the election, and his family and his campaign associates have repeatedly been negligent or untruthful about their contacts with Russian officials — most recently, in the accounts of a meeting with a Russian lawyer offering dirt on Ms. Clinton. In his first meeting as president with Russia’s foreign minister, Mr. Trump blurted out classified information. It’s reasonable to worry about what he might have told Mr. Putin.

Mr. Trump often calls investigations of his Russia ties a “witch hunt.” But the fact is that he created the swirl of suspicion. Only he can clear it up — and until he does, there will be reason for concern about any contact he has with Mr. Putin.