President Vladi­mir Putin and President Trump talk in Hamburg on July 7, 2017. (Evan Vucci/AP)

WHEN PRESIDENT Ronald Reagan sat down with Soviet leader Mikhail Gorbachev at the Reykjavik summit on Oct. 11, 1986, Gorbachev broke the ice with a wry observation that they both had brought a lot of paperwork. Did that mean something? Reagan said it was to remind each other of what happened the last time they met. The summit went on to make history. How do we know what was said? Because in addition to interpreters, both men were accompanied by notetakers, and those records, once marked “secret” and “sensitive,” are now declassified for all to see.

President Trump ought to take a cue from Reagan when he meets Friday with President Vladimir Putin of Russia on the sidelines of the Group of 20 meeting in Osaka, Japan. The notes of the meeting must be preserved under the Presidential Records Act of 1978, which covers Mr. Trump’s activities, or the Federal Records Act, which applies to agencies such as the State Department. In his previous meetings with Mr. Putin, the president has been careless about compliance. The Post has reported there is no detailed record, even in classified files, of Mr. Trump’s face-to-face interactions with Mr. Putin at five locations over the past two years. In one case, Mr. Trump seized the notes made by an interpreter who was present.

Mr. Trump should change course. He must ensure notes of his meetings are correctly maintained, because it is the law and because such records are vital for use by policymakers in his own administration, provide the basis for holding Mr. Trump to account for his actions, and are essential for historical research. Mr. Trump’s odd affinity for Mr. Putin, Russia’s interference in the 2016 presidential campaign, and the intensified hostility between Washington and Moscow all make it imperative that good records be kept. Surely, the Russians will be taking notes, too.

Proper record-keeping should not infringe on Mr. Trump’s prerogative to talk in confidence to Mr. Putin or other world leaders. Notes can be kept secret until properly declassified.

Mr. Trump’s earlier neglect also must be examined and rectified, as far as possible. Several organizations are turning to the courts, seeking to force Mr. Trump and his subordinates to follow the law. Meanwhile, Rep. Elijah E. Cummings (D-Md.), chairman of the Committee on Oversight and Reform, has renewed questions to the White House about Mr. Trump’s handling of notes during previous meetings with Mr. Putin. Mr. Cummings has asked what happened to the notes from the meeting with Mr. Putin at Hamburg on July 7, 2017, and about who in the White House might have summaries or readouts of the meetings in Hamburg and in Helsinki on July 16, 2018. Mr. Cummings says the White House has been unresponsive to earlier questions. These are legitimate issues, and Mr. Trump’s staff should stop stonewalling.

Mr. Trump may be making his own history, but he does not own it. The American people do. He cannot crumple it up at will.