Peter Zeidenberg

Opinion contributor

It appears that the Mueller investigation is reaching its endgame. After a two-month hiatus for the midterms, special counsel Robert Mueller's team is prepared to once again show its work. These developments are ominous for President Donald Trump. In short order, expect to see a case of conspiracy to interfere with the 2016 election to be laid out in court.

Defenders of the president have, despite the obvious progress of the Mueller investigation — more than 30 indictments or guilty pleas, including Trump’s campaign chairman, personal lawyer, national security adviser, deputy campaign manager and foreign policy adviser — consistently argued that “no collusion” has been proved. While it is true that the charges made public have not alleged conspiracy (there is no crime of “collusion”) it should be clear to all but the most obtuse by now that the endgame is drawing near. Mueller is laying out the predicate for a wide-ranging conspiracy case that will likely ensnare the president’s family and, quite likely, Trump himself.

Motive for why Trump curried Putin's favor

Cohen’s plea on Thursday provides a key ingredient — motive. For those who long wondered why throughout the presidential campaign Trump could not bring himself to say a critical word about Russian President Vladimir Putin, we now know the answer: Trump was hoping to do business in Russia, and doing so would require the approval of Putin.

The putative Moscow project helps provide motive for Trump to have curried favor with Putin. And once Trump repeatedly and publicly denied having any business interests in Russia, Putin had leverage over Trump, because he knew this claim was an easily disprovable lie.

Cohen’s disclosure exposes not just Trump as having lied about his business interests in Russia, it potentially also exposes his family as well. Donald Trump Jr. and Jared Kushner have both testified before Congress. We know Trump Jr. was asked about his role in negotiations about building Trump Tower Moscow, and while a transcript of Kushner’s testimony has not been made public, it is hard to imagine that he was not also asked about the Trump Organization’s business ties to Russia.

We now know that Cohen “briefed family members of” Trump about the progress of the venture. Did they testify truthfully about this? Mueller either knows or no doubt soon will find out.

The accumulation of evidence against the president seems to grow each week. Already facing potential charges of obstructing justice, Trump gave Mueller further ammunition this week when he publicly dangled the possibility of a presidential pardon for Paul Manafort, asking a reporter, “Why would I take it off the table?”

More:Donald Trump can tweet all he wants, but Robert Mueller is delivering

A web of lies and deceit: The Trump-Russia plot thickens with Michael Cohen guilty plea

If Manafort lied to Mueller, maybe he knew he had a net. Maybe it was a Trump pardon.

A better question is the one Mueller will likely ask: “Why would the president publicly dangle the possibility of a pardon in front of Paul Manafort, who Trump clearly fears will flip on him?” The answer is obvious, and it will likely add to the mountain of accumulating evidence of Trump’s intent to obstruct the investigation into his conduct, and will no doubt be included in Mueller’s final report.

Other shoes will almost certainly drop in the very near future. Mueller has informed the court that he will be filing a statement supporting his assertion that Manafort has repeatedly lied to the government while he was ostensibly cooperating with the Mueller team. Expect this filing to be detailed and fully supported by emails, phone and bank records, as well as other witness statements.

This pleading could well provide Mueller the opportunity to do an “end run” around Acting Attorney General Matthew Whitaker, who many fear would have the ability to deep-six Mueller’s report, and report directly to the court — and the public — the complete case against Manafort. After all, to establish that Manafort has lied, Mueller will have to lay out in detail what was asked, what Manafort said, and why it is that Mueller believes the responses to be false.

Don't assume Mueller investigation is safe

In other words, the endgame is likely close at hand. Answers will soon be made public. No doubt Trump senses the danger he and his family face.

As a result, no one can be sanguine that Mueller will be permitted to complete his investigation. We are one late-night tweet storm away from another “Saturday night massacre” in which Trump instructs Whitaker to fire Mueller.

Republican senators have rejected efforts to pass legislation to protect Mueller because they say that Trump is unlikely to fire Mueller since doing so would be self-destructive. The same could have been said about Trump’s decision to fire FBI Director James Comey — which is what led to the Mueller appointment.

The bottom line is that Trump’s impulsivity is intractable. The fact that something is unwise is not a deterrent for him, particularly when he is egged on by the right-wing media appealing to his sense of victimhood.

Congress should step up to publicly and loudly support Mueller, insist that the special counsel be permitted to complete his investigation, and make clear that any interference could lead directly to impeachment. Only by doing so can the public be assured that it will find out the truth about Russia’s involvement in the 2016 election.

Peter Zeidenberg, a partner at Arent Fox, spent 17 years as a federal prosecutor and was a deputy special counsel for the prosecution of Scooter Libby. Follow him on Twitter @przeidenberg