Let’s face it: The president of the United States is an agent of Russia, an enemy power. He demonstrated it for all the world to see in Helsinki on Monday, but it follows a long string of Trump actions to aid Vladimir Putin’s strategic aims.

But it remains to be proved whether Trump is a witting Putin collaborator or an unwitting (or witless) dupe. The evidence mounts that it’s the former, but it’s too early for Trump adversaries to scream “Treason!” or call for his impeachment.

What’s required is for Special Counsel Robert Mueller to complete his investigation and demonstrate a case against Trump as meticulously as he did against the 12 Russian intelligence officers indicted last week for tampering with the 2016 election to help Trump win. Only overwhelming evidence will convince a majority of the country, Republicans included, that Trump has violated his constitutional oath to defend the country and silence the Trump claque shouting that a “deep state” conspiracy is conducting a political “witch hunt.”

And it’s imperative that Democrats not blow their chance to take over the House of Representatives in November to be in a position to process Mueller’s product. Republicans, terrified of Trump’s base, cannot be depended upon to do so.

Democrats need to make it a major point of their 2018 appeals that they will provide the oversight of Trump administration policy -- across the board -- which has been near-totally lacking from the Republican Congress. And if Democrats do succeed, they need to conduct their inquiries carefully and responsibly, not engage in blatant partisan showboating, as some Republicans do. That will only deepen America’s ruinous divisions — one of Putin’s purposes systematically abetted by Trump.

It’s encouraging that some Republicans have joined in condemning Trump’s supine performance in Helsinki and in affirming their conviction that Russia interfered with the 2016 election and, as National Intelligence Director Dan Coats has said, continues to attack America’s digital infrastructure, with the 2018 and 2020 elections also in its sights. But there is little indication that Republicans will take any action — for instance, to protect the Mueller investigation from the possibility Trump will end it or threaten Trump with specific severe consequences if he does so.

Besides siding Monday with Putin against his own Justice Department and intelligence services, Trump is serving Russian ends by undermining the Western Alliance, attacking European leaders and sewing discord among European populations over immigration -- caused in part by Russia’s bombing of Syrian civilians.

He’s defended Putin’s authoritarian rule (“he’s a strong leader“) and, when asked about the murder of Putin opponents, said the United States has murdered people, too — much as Putin asserted in his interview with Chris Wallace.

He’s also systematically sewn discord within the U.S. population — including about what they can believe are facts. It’s just the kind of thing the GRU was doing in 2016, as charged in the Mueller indictment.

But, what’s the reason? Theories abound. It could be (though I doubt it) that Trump so genuinely wants good relations with Russia that he will side with Putin almost across the board. In that case, he’d be a witless or unwitting agent of Moscow. There’s a spreading suspicion that Putin “has something on Trump” and the president is being blackmailed into witting collaboration.

I share that suspicion, but it doesn’t have to do with his alleged antics with prostitutes in a Moscow hotel room in 2013, which Putin pooh-poohed in Helsinki.

My theory is that Trump has for years been up to his neck in financial deals with Russian oligarchs (maybe the mafia there, too). His son Donald Jr. confirmed in 2008 that Trump Inc. was dependent on “lots of Russian money” when it couldn’t get investments elsewhere. In 2008, during a down real estate market, Trump sold to a Russian oligarch for $95 million a Palm Beach property he’d bought for $41 million. Despite these facts, Trump has claimed he had “no deals” with Russia.

Why have we never seen his tax returns?

Putin has to know all about Trump’s financial deals and Trump knows Putin knows. Trump may be siding with the Russian leader out of fear of exposure or he may actually be a bought asset. We should all hope Mueller gets to the bottom of this — as well as whether there was direct collusion between Russia and Trump and/or his campaign to get him elected in 2016. And, if Mueller gets fired, that he delivers a report to Congress on what he’s learned.

And, that there’s a Democratic House to receive it (a Democratic takeover of the Senate is highly unlikely). Hopefully, if they do win, Democrats will be systematic and fair (though energetic) and not repeat the hyper-partisanship being shown by Republicans. (This may be a vain hope.) Trump may or may not deserve impeachment, but the Democrats must not just leap to that, but base it on thorough investigation so that a majority of Americans will agree. If they appear to be just acting out of partisanship, it’ll just further tear the country apart, serving the ends of our enemies.