And now it has come to this:

A president who has been caught up in one deception after another throughout his first few months in office quite likely crossed at least one line that, if  true, rises to the level of obstruction of justice.

A president can be impeached for that. One president, Richard Nixon, almost was. He resigned instead in disgrace.

As reported by the New York Times late on Tuesday, former FBI Director James Comey stated in a memo that he wrote at the time, on Feb. 14, that President Donald Trump had pulled him aside at the White House and asked him to kill an investigation into Trump’s former national security advisor, Michael T. Flynn.

“I hope you can see your way clear to letting this go, to letting Flynn go,” Trump said to Comey, according to the memo. “He is a good guy. I hope you can let this go.”

The White House Tuesday quickly denied the substance of the memo, but it rocked Washington, with even prominent Republicans admitting they are troubled.

Comey’s memo has a ring of truth about it, not least because he wrote it immediately after his conversation with Trump and showed it to several top aides and close friends, wanting to establish a record. They agreed not to make the memo public, however, out of a concern that it might complicate the ongoing investigation into Flynn’s possible ties with Russia and a parallel FBI probe into Russian interference in the November election.

The president’s denial that he put the arm on Comey, though, is unconvincing, in part because he has lied about other matters too often. It is difficult to say this about a sitting president, but the man lacks all credibility.

A particularly important obligation of our times is to always consider the source. Is it trustworthy or not?

Information, good and bad, pours in from everywhere, and an awful lot of people will say anything, regardless of facts. Our job, as consumers and citizens, is to separate the true from the false, the real from the fake, the honest brokers from the hucksters.

OPINION

On that score, we’re hard pressed to think of an American political leader who has failed the test of veracity worse than Trump. He just makes stuff up, and his administration is paying the price.

A president who has no credibility is a president who cannot lead.

When the Washington Post reported on Monday that Trump had irresponsibly divulged top secrets to Russian diplomats during a meeting in the Oval Office — the other big Trump story of this week — the newspaper relied entirely on anonymous sources for its story. When the White House then shot back that the story was false, you might have expected the benefit of doubt to accrue to the president. Who’s to believe unnamed sources over the word of a president?

But as Politico pointed out Tuesday, other highly credible news operations promptly passed along the Post’s story, clearly comfortable in assigning as much credibility to the anonymously-sourced allegations as to Trump’s denial; and the New York Times and Reuters quickly confirmed the story, relying on their own anonymous sources.

Much to Trump’s displeasure, this story wasn’t going away, and for good reason. The president’s credibility is all but shot, except among his most committed supporters and sycophantic media outlets such as Fox News.

Trump’s public approval rating is in the basement — below 40 percent — and his failure to play it straight has contributed to his unpopularity. A Gallup poll in April found that only 36 percent of Americans believe Trump is “honest and trustworthy.”

Trump did a particularly fine job of assaulting the truth last week when he explained why he fired Comey. First he said he dismissed Comey for the bumbled way he handled the problem of Hillary Clinton’s emails before the election, which nobody believed.

Then Trump said he would have fired Comey anyway because he’s a “showboat.” Then, still casting about for a plausible story, he said he fired Comey because of “the Russian thing.”

Bingo. You can bet Trump wanted Comey gone because of the FBI’s investigation into the Trump campaign’s ties to Russia.

But Trump also appears to have fudged the truth about Comey in other small but important ways. Most notably, the president and Comey have very different ideas about who said what at a dinner the two shared in January. Trump would have you believe Comey begged for his job. Comey says Trump inappropriately demanded a personal pledge of loyalty, which Comey says he refused to give.

Trump could settle the matter by releasing recordings of the conversation, which he has hinted may exist. But the president, true to form, now refuses to confirm or deny there are any recordings.

When Trump behaves so rashly, he risks doing harm to our nation’s best interests. Certainly, there’s an excellent case that he did just that last week during his meeting with the Russian diplomats.

According to the Washington Post, Trump disclosed intelligence about an Islamic State terrorist plot that had been obtained from a confidential source. The president had not asked permission from the source to pass along the intelligence to the Russians, and he may have inadvertently outed the source by doing so.

On Tuesday, the New York Times reported the source was Israel, which put a good face on the matter. Ron Dermer, the Israeli ambassador to the United States, said the two countries would continue to work closely together.

That was the diplomatic thing to say, of course, though the Israelis may be quietly seething.

In any event, Israel has new reason to be wary of taking this American president at his word, as do the American people.