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Our leaders have gotten us entrapped in the most topsy-turvy impeachment case in American presidential history.

Most of us are quite sure about what President Donald Trump really did — or didn't do — that has landed him in the middle of this impeachment crisis. And you don't even need a spoiler alert to know how it is going to come out: Trump will very likely end up with his presidency forever tarnished by impeachment in the Democratic-controlled House, but then never be convicted by a required two-thirds vote of the Republican-controlled Senate.

But even though we already know how this story will end, we also know we haven't seen the unmistakable, unimpeachable evidence that can prove beyond all doubt whether either that impeachment outcome or that final nonconviction verdict will be absolutely justified.

For we all know better evidence is available and get-able — but we haven't seen it yet and may never see it before the final votes are cast in the House and Senate.

There's no "smoking gun" tape recording. And no stained blue dress. Indeed, we've seen nothing that's even close to those two very different forms of self-incriminating evidence that brought shame and disgrace to two recent presidents. (We haven't heard or read recorded words like those in which Richard Nixon planned and ordered the coverup of crimes he told us he hadn't even known about; that proof of guilt led him to resign in the face of certain impeachment and conviction. Also, no one has discovered evidence like that unlaundered dress that scientifically proved Bill Clinton lied under oath about sex that he swore to us never even happened; that proof of guilt led to his impeachment in the House but nonconviction in the Senate.)

But this week, the Democrats who control the House Judiciary Committee — in their rush to have a House impeachment vote before Christmas — may have missed a gift-wrapped opportunity to press for new and far more convincing evidence of Trump's impeachable crimes. Their gift opportunity was placed before them by the Republicans' only witness in Wednesday's panel of four constitutional law experts on the topic of impeachment. At issue was whether Trump had demanded that Ukraine's new president, Volodymyr Zelensky, must agree to begin two probes of Trump's Democratic opponents in order to receive the $391 million in U.S. military aid that Trump had ordered frozen. Ukraine, which is under attack from Russian-backed troops, was desperate for the U.S. aid.

George Washington University Law School's well-known Prof. Jonathan Turley pointedly didn't contend in his testimony that Trump never demanded a quid pro quo from Zelensky. (Lower-level officials have testified Trump was insisting Ukraine probe Democratic presidential front-runner Joe Biden's son, Hunter, who was hired at a huge salary by the Ukraine gas company called Burisma. Trump also reportedly wanted Ukraine to probe whether Ukraine was involved in trying to influence the 2016 U.S. presidential campaign.)

Indeed, Turley only testified that the Democrats had failed to obtain the best possible evidence from the top-level officials who had direct knowledge of what Trump was demanding. Indeed, Turley said if Trump had demanded that quid pro quo, it would be grounds for impeachment.

But the Democrats largely ignored Turley's testimony and mainly questioned the other three professors who seemed to be progressive Democrats, had contributed to Democratic campaigns and testified Wednesday there was already enough evidence that Trump had insisted upon that quid pro quo.

Democrats could have asked Turley which Trump senior officials he thought should be subpoenaed to testify to help the Trump White House best present its complete story. They might have suggested — and Turley likely would have agreed — that Trump's chief of staff Mick Mulvaney, former national security adviser John Bolton, and Secretary of State Mike Pompeo (all of whom had refused to testify) would make the most credible witnesses.

Remember: Mulvaney recently told White House reporters that Trump was of course making quid pro quo demands as part of his policymaking — famously adding "get over it!" Also, Bolton, who reportedly opposed any quid pro quo demands on Ukraine before leaving his Trump job, apparently is willing to tell it like it is — he just signed a $2 million book deal. It is unclear whether Bolton will tell his story to Congress, pro bono, just as a good citizen.

Democrats could then have urged the committee Republicans to heed the recommendation of the Republicans' own witness and join the Democrats in a bipartisan effort to get the best possible witnesses. Of course that's an offer the Republicans were bound to have refused.

Those Americans whose minds are not precast in preconceptions could only have been impressed that Democrats were making best-faith efforts to get the best possible evidence.

Martin Schram, an op-ed columnist for Tribune News Service, is a veteran Washington journalist, author and TV documentary executive. Readers may send him e-mail at martin.schram@gmail.com.