Once again, “smoking gun” evidence that seems to incriminate a Republican president has been uncovered – and once again, it turned up in a way that was indeed inconvenient for Republicans in Congress.

Perhaps it’s a pattern that is going to occur every 45 and a half years.

It first happened in the summer of 1974, when President Richard Nixon’s “smoking gun” audio tapes were made available to impeachment investigators thanks to a unanimous Supreme Court order. Politically loyal but highly patriotic members of the Republican Party had already voted against resolutions to impeach the Republican president, when that new evidence showed up. Suddenly they were confronted with audio taped evidence of Nixon actually planning the cover-up of the Watergate crimes he had denied even knowing about. And 10 patriotic House Judiciary Committee Republicans who had just voted against Nixon’s impeachment quickly switched their votes. Then three Grand Old Party elders, Sen. Barry Goldwater, R-Ariz.; Sen. Hugh Scott, R-Pa.; and Rep. John Rhodes, R-Ariz., drove 16 blocks down Pennsylvania Avenue and told Nixon his Republican support had vanished and he faced certain House impeachment and Senate conviction. And Nixon resigned.

This week, another type of “smoking gun” evidence stunningly surfaced after the Democratic House had voted to impeach President Donald Trump, with all House Republicans voting no, supporting their president. The case is now before the Republican controlled Senate, which seems determined to acquit Trump – new evidence be damned. This new evidence surfaced in a form and way that was decidedly different from the tapes and transcripts of 1974, yet still very significant. It surfaced not because of a high court order, but because of converging forces at the intersection of politics, governance and the book publishing industry. And the evidence came not on a form where Republicans can hear their president admitting anything – but they can read the words of their most hardline international policy ideologue, their fellow Republican John Bolton, Trump’s former national security adviser.

In a politically earth-shaking scoop, The New York Times reported last Sunday night that Bolton wrote in an upcoming book that the president admitted to him that he was demanding Ukraine provide him with the very quid pro quo Trump swears to us never happened. His book, now set to be published in March, reportedly says Trump admitted insisting that Ukraine must announce the start of an investigation into Trump’s leading Democratic presidential challenger, Joe Biden, and his son Hunter. Biden’s son was paid big bucks to work for a gas company called Burisma. In return, Trump said, he would give Ukraine the $391 million in congressionally approved military aid he had ordered frozen. Never mind that Trump was legally required to give Ukraine the military aid without insisting upon a political favor.

Faithful readers may remember that just a week ago, on Jan. 22, I wrote a column headlined “Unbolting Bolton.” I made the case that, while I didn’t know what Bolton may have written in his upcoming book, we knew his publisher, Simon & Schuster, reportedly was paying Bolton $2 million. Well, publishers don’t pay that kind of money for a tell-all that won’t tell all. (Frankly, Biden needed to either tell Hunter to quit his job, or Biden needed to tell President Barack Obama he had to quit working on Ukraine matters because of his son’s new job.)

In that column, I said Bolton and his publishers will be lambasted if they keep any big revelation secret, allow Trump to be acquitted – and then publish the book revelations that Bolton withheld. I contented Bolton needed to say what he knows for free – now! Write an op-ed, give an interview or just leak it.

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And lo, it came to pass – somehow. The Times scoop reported that Bolton had given Trump’s national security council a draft of the book so they could make sure it contained no inadvertent classified material.

So how did today’s New Generation of Republican leaders and followers respond to the report about Bolton’s de facto “smoking gun” evidence? Did they respond as patriotically as their Republican ancestors did back in the Nixon era? Did they quickly move to subpoena Bolton as a witness so he could provide his de facto “smoking gun” evidence to Trump’s Senate impeachment trial?

No way. Senate Majority Leader Mitch McConnell and his team made clear they were determined to fight any effort to subpoena Bolton as a witness or explore any new evidence that could implicate the president, no matter what. McConnell, after all, had boasted about consulting on impeachment strategy with Trump’s White House – then raised his right hand and swore he’d provide “impartial justice” in leading the Senate impeachment trial.

If McConnell gets his way, there will be no profiles-in-courage in history’s chronicling of his iron-fisted command. Indeed, McConnell is all about making sure his profile casts no shadow on the marbled Capitol steps.

Martin Schram, an op-ed columnist for Tribune News Service, is a veteran Washington journalist, author and TV documentary executive.