Even without the widening scandal over election interference, President Trump would have had a hard time managing America’s relations with Russia, which are as tense as at any time since the end of the Cold War.

The complex differences between the two countries will not be easily resolved. Moreover, President Vladimir Putin has shown a ruthless commitment to self-preservation that relies heavily on returning Russia to a mythical place of power and glory, not in helping the West build a more stable world.

Mr. Trump is making sound policy making even harder, though, with his admiration of Mr. Putin and his willingness to surrender the country’s international leadership, which was on display during the Group of 20 meeting in Germany. Mr. Trump is noticeably more comfortable with Mr. Putin than he is with most of America’s democratic allies, despite Mr. Putin’s record of crushing domestic opponents, invading Ukraine and bombing civilians in Syria.

There is nothing wrong with Mr. Trump’s ambition to improve relations with Moscow, given Russia’s importance as a nuclear weapons superpower with a United Nations Security Council veto. But that does not mean it is wise to underestimate, as Mr. Trump seems to do, the threat posed by Mr. Putin’s efforts to weaken NATO and the trans-Atlantic alliance, subvert democratic procedures and institutions in Europe and America, wage cyberwarfare, destabilize Ukraine and secure influence in Syria. Some Trump administration officials recognize those hazards; Mr. Trump does not.