Jeff Stein is a longtime Washington-based national security reporter and the author of “A Murder in Wartime: The Untold Spy Story That Changed the Course of the Vietnam War.”

‘Wow,” Michael McFaul, a former U.S. ambassador to Moscow, exclaimed on Twitter in late October. “We still need to understand why Trump remains so intent on appeasing Putin.”

What set off McFaul was testimony from a top State Department official that “senior officials in the White House” had blocked the department from condemning Moscow for attacking Ukrainian ships in the Azov Sea. And on that day it was telling that even McFaul, a Kremlin-watcher for nearly 40 years, was struggling to put his finger on exactly what had driven the president of the United States into the Russian strongman’s arms, tugging the Republican Party along with him.

Trump’s affinity for Vladimir Putin seemed to glow red during a now-notorious 2018 Helsinki news conference when he sided with the former KGB agent’s denials of election interference over U.S. intelligence agencies’ findings. But so much else has erupted before and since, from revelations that he was secretly pursuing a Moscow hotel deal during the 2016 campaign, to exposés of his business relations with Russian oligarchs, to his continuing criticism of the NATO alliance, to his acquiescence to Russian troops taking over abandoned U.S. bases in Syria, to his pressure on Ukraine’s president to say publicly that Kyiv, not Moscow, had hacked the computers of the Democratic National Committee.

It makes you wonder, as the TV detectives say. Now comes Malcolm Nance, a former U.S. Navy counterterrorism specialist turned regular MSNBC Trump basher, seeking to expose the underside of the Trump-Putin relationship. Like everybody else who’s plowed this ground — including the FBI, whose controversial counterintelligence case on the Trump campaign came under sharp scrutiny from the Justice Department inspector general — Nance hasn’t resolved the question. Instead, in “The Plot to Betray America,” he’s gathered up scraps of evidence to make a persuasive, if circumstantial, case that the president is indeed Moscow’s man in Washington. In essence, it’s a progress report in a mole hunt.

Why do once-loyal men go bad? Mole hunters have an acronym for it: MICE, which stands for money, ideology, coercion/compromise and ego/excitement. Trump qualifies for three out of four, in the telling of Nance (and many others who’ve long followed Trump’s career), that explain his attachment to Moscow. Ideology’s not one of them, notwithstanding Trump’s crude nationalist populism that in many ways apes Putin’s kleptocratic rule. According to New York state records revealed by the Smoking Gun, he changed party registrations at least five times over the years.

He did, however, get caught up in the mid-1980s “Gorby fever” (as New York Times columnist William Safire mocked it) that swept the world when Russian leader Mikhail Gorbachev and President Ronald Reagan began negotiating nuclear arms reduction agreements. In typical Trump fashion, of course, he thought he, the great dealmaker, could finish the job single-handedly. As Nance writes, Bernard Lown, a Nobel Peace Prize winner, asserted that Trump said if Reagan would let him do it, “within one hour the Cold War would be over.” Trump “had Russia mania in 1986,” Lown said. In 1987, he was in Moscow scouting construction sites.

On his arm was his first wife, Ivana, a native of communist Czechoslovakia, whose Moscow-controlled spy service, the StB, had long counted her father as an informant, according to authoritative reporting cited by Nance. Her 1977 marriage to Trump had prompted the Czechs to open a dossier on him. “We knew that Trump was influential. He didn’t hide that he wanted to become president one day,” the StB’s then-chief said years later. “We were interested in learning more things about him.”

Especially his weaknesses. In Trump, they found two, a hunger for money and a raging ego, not to mention a lust for beautiful women. They began dangling opportunities — the Miss Universe contest, Trump Tower Moscow. They treated him like a potentate, affording him the bedroom suite reserved for princes and presidents at the Moscow Ritz-Carlton. Then, in the wake of Trump’s Atlantic City bankruptcies, Nance recounts, Trump found new sources of cash from Russian sources, including the Kremlin-connected Deutsche Bank, Russian oligarchs who bought luxury condos in Trump Tower and “New York City allies from the former Soviet Union” who partnered with him in real estate deals from SoHo to Baku. One of them, Felix Sater, would eventually be accused of laundering hundreds of millions of dollars stolen from a Kazakhstan bank “to develop a Trump Tower in Moscow,” according to a lawsuit reported by the Associated Press.

That Trump wanted the details of his financial sources kept secret (along with his tax returns) was all the better, Nance notes: It gave Putin a better hold on him, a tool for coercion.

From the beginning, Russia had used “the MICE strategy to bring him under its sway, as his interest in Russia clearly blinded him,” Nance theorizes. “He was a potential asset and an exploitable victim worth keeping.”

Judging by his Russia-related decisions and pronouncements, the strategy has worked. Trump has dismissed Moscow’s subversion of American politics and pursued debunked conspiracy theories tying Ukraine to Hillary Clinton’s campaign. Equally important to Moscow’s strategic goals, he’s disparaged NATO and, by championing Brexit, undermined the European Union.

To longtime observers, Trump’s transformation of the GOP from hard-line cold warriors to muted bystanders has been astounding. Here again, Nance points to the possible role of foreign money, citing a Dallas Morning News report that Russian oligarchs and front groups provided millions of dollars for the campaigns of key Republican senators.

All in all, Nance has produced an impressive clip job, assembling scores of reliable media reports, congressional hearings and the findings of special counsel Robert Mueller’s investigation into a persuasive whodunit narrative. Alas, it remains a circumstantial case. It’s a prosecutor’s pitch to a jury of millions of Americans who don’t get to vote for almost another year.

The Plot to Betray America

How Team Trump Embraced Our Enemies, Compromised Our Security, and How We Can Fix It

By Malcolm Nance

Hachette. 358 pp. $28