Ron Johnson’s public image is that of a delusional conspiracy theorist who struggles to pull together coherent sentences. But in his real work as a United States senator he suddenly becomes precise and proficient.

That work, as the Wisconsin Republican has made clear since arriving in Washington more than a decade ago, is principally to redistribute wealth upward. Johnson, a millionaire many times over, is not averse to enriching himself. But his most ambitious legislative endeavors have often involved the augmenting of the bank accounts of his political benefactors.

The latest evidence of Johnson’s perfidy comes in the form of a ProPublica study that examines the scandal-plagued senator’s machinations during the fall 2017 battle over tax “reforms” that had been proposed by the Trump administration and its congressional allies. What Trump was proposing was a $1.5 trillion giveaway to the rich, precisely the sort of plan that Johnson had backed since his election to the Senate in 2010 as the blandest member of the “Republican wave.”

Inexperienced and inarticulate, Johnson settled comfortably into the back benches of the Senate, doing as he was told by Mitch McConnell and keeping such a low profile that, as his first six-year term finished, polls showed most Wisconsinites had no opinion regarding the man who had replaced one of the Senate’s ablest progressives, Russ Feingold.

When Donald Trump arrived on the scene, Johnson came alive. He even talked up the prospect of campaigning in 2016 as “the Ronald and the Donald.” After the election, Johnson enthusiastically backed the agenda of the new Republican president. In November of 2017, however, the senator suddenly broke with the president, as the ProPublica study recounts. At a critical stage in Trump’s push to secure approval of the tax plan, Johnson announced that he was going to vote against it.

“Making the rounds on cable TV, the Wisconsin Republican became the first GOP senator to declare his opposition, spooking Senate leaders who were pushing to quickly pass the tax bill with their thin majority. ‘If they can pass it without me, let them,’ Johnson declared,” recounts the ProPublica report.

Johnson had not suddenly developed a conscience, and he certainly was not aligning with the Democrats who decried the Republican plan as what it was: a scheme to make the very rich very much richer. The Wisconsinite was playing politics. And, despite his bumbling image as a legislator so inept that a home-state website labeled him “our dumb senator,” Johnson was maneuvering rather skillfully. According to the new study,

Johnson’s demand was simple: In exchange for his vote, the bill must sweeten the tax break for a class of companies that are known as pass-throughs, since profits pass through to their owners. Johnson praised such companies as “engines of innovation.” Behind the scenes, the senator pressed top Treasury Department officials on the issue, emails and the officials’ calendars show.

Within two weeks, Johnson’s ultimatum produced results. Trump personally called the senator to beg for his support, and the bill’s authors fattened the tax cut for these businesses. Johnson flipped to a “yes” and claimed credit for the change. The bill passed.

Why did Johnson fight so hard against a president for whom he has generally been willing to debase himself as the most willing lapdog in the Senate Republican Caucus? At the time, Wisconsin media speculated that “Johnson Wants a Bigger Tax Cut for Himself.” There was certainly something to that argument. But it turns out that, in this particular instance, Johnson was not just thinking of himself.

Confidential tax records, obtained by ProPublica “reveal that Johnson’s last-minute maneuver benefited two families more than almost any others in the country—both are worth billions and both are among the senator’s biggest donors. Dick and Liz Uihlein of packaging giant Uline, along with roofing magnate Diane Hendricks, together had contributed around $20 million to groups backing Johnson’s 2016 reelection campaign. The expanded tax break that Johnson muscled through netted them $215 million in deductions in 2018 alone, drastically reducing the income they owed taxes on. At that rate, the cut could deliver more than half a billion in tax savings for Hendricks and the Uihleins over its eight-year life.”

Even for the billionaire class, that’s an epic windfall.

Johnson, who was worth around $40 million before the pandemic, has a long record of voting for legislation that benefits the owners of so-called “limited-liability” corporations, like the one he owns with his wife. But as the political outsider has become a political careerist, he has expanded his grifting to serve the interests of those who have kept him in office up to this point.

Johnson has not announced his bid for reelection in 2022, but there are growing signals that—despite a promise to limit himself to two terms—he will run again. It will be a tough race for him, so he’ll need all the billionaire backing he can get to explain away his reputation as a conspiracy theorist who embraces Trump’s Big Lie about the 2020 election and rejects science when it comes to the coronavirus pandemic.

The Democrats in Wisconsin seeking Johnson’s Senate seat have already seized on the latest revelation of the his crooked abuses of power. “Ron Johnson used his office to enrich some of his wealthiest campaign donors while raising taxes on the middle class and widening the income inequality gap,” declared Wisconsin Lieutenant Governor Mandela Barnes. Recalling that Johnson tried to block the $1,400 survival checks for struggling families at the height of the pandemic, state Treasurer Sarah Godlewski described the senator as “a cash cow for billionaires and a disaster for Wisconsin workers and families.” But Outagamie County Executive Tom Nelson may have summed the circumstance up best when he observed, “Johnson took $20 million from Wisconsin’s wealthiest right-wing billionaires, then fought to get them gigantic tax breaks. He’s not a fiscal conservative, he’s a corrupt errand boy for the ultra rich.”