Precedents abound in a country whose first presidential election took place 230 years ago. Three of our 44 presidents have faced impeachment proceedings — Andrew Johnson, Richard Nixon and Bill Clinton — and now it seems Donald Trump will be the fourth.

Democrats have been itching to oust Trump from office since election night nearly three years ago. High law-enforcement and intelligence officials started trying to keep him from the White House months earlier and for three years pushed the theory that he and his campaign were acting in collusion with Russia.

Collusiongate finally collapsed, in the words of New York Times editor Dean Baquet, “the day Bob Mueller walked off that witness stand,” when “our readers who want Donald Trump to go away” realized that wasn’t going to happen.

So, now, we hear that a whistleblower had been told Trump abused his powers in a telephone conversation with the president of Ukraine. On Tuesday, Trump announced he would release the transcript, and Speaker Nancy Pelosi announced that the Democratic-majority House was officially considering impeachment.

The transcript doesn’t read exactly as the still-anonymous whistleblower had claimed. Trump asked the newly installed Ukrainian president to investigate 2016 anti-Trump efforts there.

Democrats claimed Trump offered a quid pro quo by suggesting he’d released US aid he’d been holding up. But Trump said nothing about that. Given his broad powers, any request the president makes of a foreign government could be called a threat.

On Collusiongate, Democrats followed the Nixon precedent, allowing a special prosecutor and congressional committees to conduct long investigations, with numerous leaks to sympathetic media. That produced evidence that made impeachment certain, and Nixon resigned. But Collusiongate didn’t follow precedent.

Now Democrats seem to be following the Andrew Johnson precedent. Johnson’s Republican critics hated him for obstructing equal rights for free blacks and for his vitriolic and scurrilous oratory.

Proceedings began on Feb. 24, 1868. The House voted for impeachment on March 3, and on May 16, the Senate voted 35-19 against him, 1 vote short of the two-thirds majority needed to remove him from office.

So, Democrats’ course is, as my Washington Examiner colleague Byron York puts it: “Move fast. Don’t withhold judgment. And don’t wait for the results of a long, ponderous investigation.”

Pelosi seems primed to push for a quick vote as soon as 218 yeas are in sight. But in the 53-47 Republican Senate, absent new facts or changed public opinion, there are far fewer votes for removal than in 1868.

Polling shows voters oppose impeachment by nearly 2-1 margins, similar to when Bill Clinton was impeached in 1998. Both parties thought impeachment would help them politically.

Clinton’s job approval rose sharply, but his personal ratings slumped badly. The former helped keep him in office, while the latter hobbled his chosen successor, Al Gore, two years later.

Speaker Newt Gingrich forecast big gains, but Republicans lost four seats in November 1998, and Gingrich lost his speakership. But Republicans held on to their House majority that year and in the next three congressional elections.

Those largely positive results reflect late 1990s contentment and the fact that both parties had intellectually serious arguments in line with their values. Republicans argued that Clinton’s lies in a federal court proceeding violated his constitutional duty to faithfully execute the laws. Democrats argued that his offense was only a personal matter unrelated to his official duties.

Trump’s support has remained impervious to charges of personal or professional misconduct, just as his detractors remain impervious to claims that his policies have been successful. What could hurt Democrats in times of discontent, when impeachment is unpopular, is their opportunism in seizing on any excuse to vent their rage. The Ukrainian phone call is much smaller potatoes than collusion with Russia would have been.

But Democrats “who want Donald Trump to go away” just couldn’t wait to let voters make that choice. They risk four more years of angry frustration.