Newton’s third law of motion states that in nature for every action there is an equal and opposite reaction. It can operate in politics, too. Or as Harvard law professor Jack Goldsmith recently wrote, “It is part of Trump’s evil genius that he elevates himself by inducing his critics to behave like him.“

Call it Trump Derangement Syndrome, and recognize it for what it is: something that could end up snatching defeat from the jaws of victory for the Democratic Party once again in 2018 and 2020.

Signs of that possibility are apparent in the polls. President Trump’s job approval has remained low, by historic standards, but it has also remained pretty steady — and has been rising, just a bit, in recent weeks.

The standard pattern has been for presidents to start off their term with high honeymoon ratings, then sag somewhat in their second years unless buoyed (as both Presidents Bush were) by perceived foreign policy successes.

Absent that, what followed in the midterm elections of 1994, 1998, 2006, 2010, and 2014, was the opposition party winning majorities in both houses of Congress (except for the Senate in 2010).

Trump’s trajectory has been different. After his barbed tweets and controversial campaign, surprise win, and revelation of the Clinton-campaign-financed Steele dossier, he was never in honeymoon territory. His average job approval in the realclearpolitics.com average never topped 46 percent — the same percentage he won in the popular vote against Hillary Clinton.

In the months that followed, his numbers oscillated within a narrow range, and often with no discernible (to the press, anyway) connection with events. As in the 2015-16 campaign, stories that would have hurt other politicians (Stormy Daniels, anyone?) seemed to have been priced in on attitudes toward Trump. You loved him or you hated him, and you kept on doing so.

Trump's recent upswing has his approval at 43.5 percent — well below 50 percent, but far higher than the 35 percent President George W. Bush had before the Republicans’ “thumping” in 2006.

Perhaps this reflects the economic upswing since the Republican tax bill passed in December. Perhaps it reflects presidential initiatives on Korea, Iran, China, or the respect shown him by the leaders of France, Saudi Arabia, Japan, Germany, and others. He may be uncouth, some may think, but he’s getting results.

And perhaps it reflects the Democrats’ Trump Derangement Syndrome.

You had the spectacle of every Democrat on the Senate Foreign Relations Committee and 42 Democrats on the floor opposing Trump’s nominee for secretary of state — a nominee, Mike Pompeo, for whose confirmation as CIA director some of them voted and who has been getting good marks at Langley.

That’s as unprecedented as Trump’s insulting tweets, and less fact-based than many of them, too. Some Democrats complained about Pompeo’s stands on gay issues. But they’re the party that blocked for seven months the nomination of a gay ambassador to Germany, Ric Grenell.

Another spectacle of Trump Derangement Syndrome was last Saturday’s White House Correspondents' dinner where a comedienne’s vitriolic monologue and mean-spirited attacks on the physical appearance of Trump’s press secretary validated his decisions this year and last not to attend. The event only further undermined the credibility of the anti-Trump press.

Its credibility may be further reduced if, as seems likely, special counsel Robert Mueller’s investigation ends with no finding of “collusion” between Russia and the Trump campaign. Mueller’s questions for the president leaked to the press, if accurate, indicate that he has reluctantly concluded as much and is looking now for evidence that he can spin up as obstruction of justice.

Much of the press, notably CNN, have treated the Russian collusion story as a second Watergate, and many Democrats amuse their friends with little quips assuming Trump administration policy is set in Moscow. It's not very funny any more.

The “collusion” that seems more likely to have occurred is between President Barack Obama administration intelligence and law enforcement personnel and the news media to push the Russia collusion story largely or solely on the evidence of the Clinton-financed Steele dossier.

Meanwhile, House Democratic leaders Nancy Pelosi, D-Calif., and Steny Hoyer, D-Md., try to hush candidates who are baying for impeachment to meet the demands of party megadonor Tom Steyer and majorities of Democratic voters.

They try to tilt local Democratic primaries toward candidates with military or law enforcement backgrounds and against #resistance types visibly afflicted with Trump Derangement Syndrome.

Looking ahead, it’s possible that Republicans in 2018 and President Trump in 2020 could win based on solid achievements. But their chances will be better if Democrats can’t shake off their bad case of Trump Derangement Syndrome.