Many critics of President Trump, including a sizable number of Democrats in the Republican-controlled Congress, are wary about the incipient congressional investigations of Russia’s interference in the 2016 presidential election and the possibly related Russian entanglements with the Trump administration and campaign. They suspect that an independent investigation from outside the government is the only hope for checking a president who seems oblivious to press criticism, whose party controls Congress and who has the executive branch under his thumb.

These worries are understandable but misplaced. There might be a time when an independent investigation becomes necessary, but we are not nearly there yet. For now, our constitutional system is working well to ferret out the truth and to hold Mr. Trump and his subordinates accountable.

The most important checks on the Trump presidency come from inside it. The Federal Bureau of Investigation is reportedly conducting at least three investigations related to Russia, the election and the administration. Whatever one thinks about his pre-election maneuvers, the F.B.I. director, James B. Comey (a former colleague of mine at the Justice Department), has proved to be an independent actor, and he has every interest in pursuing the cases wherever they lead.

Mr. Trump could fire Mr. Comey on a whim, but that would not kill the F.B.I. investigation. Rather, just as President Richard Nixon hastened his impeachment with the Watergate-related firings known as the “Saturday Night Massacre,” canning Mr. Comey would only heighten the public’s and Congress’s suspicions about Mr. Trump’s guilt and increase pressure on the F.B.I. and others to get to the bottom of the Russia matter.