WASHINGTON — As Donald Trump wreaks havoc in both domestic and foreign policy with his governing by impulse and bias, the Justice Department investigation into Russian election meddling remains a darkening cloud over his presidency.

His threats of a trade war with China, of military confrontation with North Korea and of using National Guard troops on our southern border raise heightened talk of impeachment among Trump critics, looking to Special Counsel Robert Mueller to provide the grounds.

These Trump rivals seem split between wanting Mueller to take his time in making a foolproof case against the president and coming up with his results as soon as possible, before this president does further damage to American democratic values and institutions.

Those who fervently hope or expect that Mueller will find proof of personal Trump corruption or collusion with the Russians in the 2016 presidential election are pointing toward November’s midterm congressional election as the vehicle for ousting him.

They see a “blue wave” coming in which Democrats will take over the Republican-held House, where the process of impeachment must start. History demonstrates that the first midterm election in a presidency favors a majority for the out-party.

A public campaign led by California billionaire Tom Steyer pushing for impeachment appears to be gaining steam from an expensive television ad in which he argues that time is of the essence, considering in his view the damage Trump is inflicting on the country.

Many congressional Republicans, following the lead of House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell, have so far rolled over in acquiescence to Trump. They appear intimidated by his grass-roots support and/or fear of personal wrath from his famous temper and prolific tweets.

A likely result is that these midterm elections, often decided by local issues and the incumbents’ records in their congressional districts, inevitably will be seen as a broad referendum on Trump himself, with frustrated and outraged Democrats coming out of the woodwork in droves to get rid of him, and on the Republican Party.

Despite the heat and hostility that this president has generated on both sides in only his first year in office, the path to impeachment in the House, and more significantly to conviction in the Senate, is far from certain. In the nations’ history, only two presidents — Andrew Johnson in 1865 and Bill Clinton in 1998 — were ever impeached by the House, and both were acquitted in the Senate acting as the jury.

Johnson was impeached for firing Abraham Lincoln’s secretary of war, Edwin Stanton, in violation of the Tenure of Office Act, and he was acquitted by a single vote in the Senate. Clinton in 1998 was similarly saved by Democratic senators holding their noses and bailing him out of a sordid sex scandal by keeping the majority vote for conviction short of the required two-thirds of the Senate.

With today’s Senate still narrowly in Republican hands, the Democrats would need to gain only two seats in November for a majority, but they would need many more to muster two-thirds to convict an impeached Trump. The resultant chaos of such a partisan confrontation can only be imagined at his point, dependent on just what the Mueller investigation finally yields, and the willingness of Senate Republicans to stand by Trump by then, if accused and impeached.

All this makes for further political havoc in the country, which is already deeply divided over this most unconventional and unpredictable of American presidents in its history. Rather than have Mueller rush to judgment now, the nation’s best interest will be served by his continued deliberate plodding to learn all the truth about this sordid affair of Russian intervention in our cherished electoral process.

Now that the investigation is going forward on two fronts, the other being into shady personal business dealings in New York by other federal prosecutors, Donald Trump’s guilt or innocence, not to mention his ability to run the country in such perilous times, grows more worrisome with every passing day.

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