Ask a professional Democrat for his or her opinion on billionaire political donor Tom Steyer, and the answer you often get is a variation of the following: Why would someone with so much money spend it all on a fruitless attempt to impeach Donald Trump?

Press them for their thoughts in private, however, and many concede that the man funding a $40 million campaign to get rid of the current president is not just a gifted self-promoter, but is, in fact, building one of the true powerhouse entities within the Democratic ecosystem. Steyer is poised to play a massive role in the midterms and pull the party in the direction of his choosing. He’s also set himself up incredibly well—perhaps better than any other potential aspirant—for a serious presidential bid in 2020.

“If I were a rich person and I wanted to run for president,” said one top Democratic strategist, “I would be doing exactly what he’s doing.”

What Steyer is doing is acquiring the equivalent of prime political real estate. Through his self-funded Need to Impeach campaign, he has now built an email list of more than 5.1 million members, a total that one former presidential campaign manager called “staggering” and a top digital adviser called “one of the biggest Democratic lists out there.”

Perhaps even more remarkable is how Steyer came about doing it. Kevin Mack, the lead strategist on the impeachment campaign, said the first million members signed up in just six days. He added that open rates remain high—“probably at least double the industry standard”—allowing them to take two to three campaign actions at a given time. Approximately 1,975,000 of those on the list are identified as infrequent midterm voters.

“They care more about digital than the DCCC and the DNC,” said one of the party’s top digital strategists.

As formidable as Steyer’s data operation is, there may still be room to grow. The group has only spent one-third of its budget on digital and, according to Mack, its typical email list member is an elderly woman—a reflection of the cable-heavy ad focus but also an indication that a younger, internet savvy demographic is still there for the taking.

Even Republicans are impressed. Bill Whalen, a research fellow at the Hoover Institution and a former adviser to California Republicans including former Govs. Arnold Schwarzenegger and Pete Wilson, thinks the emerging voter database portends a potential presidential bid.

“I look at Tom Steyer and I see what is the equivalent of Cambridge Analytica,” Whalen told reporters at a Hoover conference on Sunday, referring to the Trump-aligned firm at the center of controversy over the use of allegedly pilfered Facebook data. Whalen wasn’t suggesting that Steyer has engaged in similar malfeasance but simply that his data-centric operation is a potent political force.

“He is collecting signatures and he is building a potential voter database, which puts him in a rather interesting spot for 2020,” Whalen added. “I don’t know where impeachment goes if the Democrats get the House, but he’s been there from the beginning of that topic.”

In an age when the political parties are growing less influential, Steyer has, in essence, built a mini-party of his own. By latching on to the issue of impeachment, he has become both a leading figure in the resistance movement and the standard bearer for how anti-Trump a presidential candidate can and should be. Allies say he’s tapping into the sense among Democrats that their country is being taken away. More neutral observers hear echoes of how birtherism was used against President Obama, albeit absent the racist dog whistles and lack of sophistication.

“He is using Trump the way Trump used Obama,” said Tad Devine, a top Democratic operative who helped run Sen. Bernie Sanders’ (I-VT) presidential campaign. “It as an organizing point. There is so many people who dislike Trump at such a basic level that that is the single most popular issue out there… The guy has an ability to repel voters like nothing else out there, and if you can be associated with taking him on, it is a big deal.”

Steyer’s team is hardly coy about his political ambitions. Mack confirmed that Steyer not only eyed a run for California governor and Dianne Feinstein’s Senate seat, but also polled how he would do in those contests. The results aren’t known. But Mack did reveal that among those on the Need to Impeach mail list, Steyer enjoys an 89 percent name recognition and an 86 percent popularity rating.

“Tom’s number one priority is winning back the House in 2018. We see that as the first step in the impeachment process,” said Mack. “If that doesn’t occur, I think Tom will look at all his options and make the decision he thinks is best for the country.”

What Steyer has in money, issue appeal, and email addresses, however, he lacks in political roots. He cut his teeth at the hedge fund Farallon Capital Management, which he founded in 1987 and led until 2012, when his net worth was pegged at $1.3 billion (Forbes now estimates it’s $1.6 billion). It was only in 2014 that he fully thrust himself into federal electoral contests, but he quickly became by far the largest political donor in the nation. Initially, his focus was almost exclusively on climate change. But his ad campaigns had limited success, and Steyer’s preferred candidates lost a majority of the federal elections in which he got involved in the 2014 and 2016 cycles.

He didn’t drop the climate focus. He just added impeachment into the mix. At first, it was merely in bringing up the topic during media hits. Elected Democrats begged him to stop. But a source close to Steyer said he was amazed at the feedback he’d get for those hits, which, in turn, convinced him that there was a strong political appetite for the issue. And he didn’t half-ass it. Mark Putnam, widely considered one of the top ad men in Democratic politics, has produced the TV spots, while top party officials such as Bruce Reed (Joe Biden’s former chief of staff) and Chris Lehane (Al Gore’s former press secretary) have previously served as advisers.

Steyer’s critics—and he has a few, all of whom would rather not have their thoughts on the record—argue that the campaign is a political vanity project, one that doesn’t poll well among the broader public and could deeply damage the party’s messaging during the midterms. But even they concede that there is a maddening ingeniousness to it.

“I think he is someone who thought about running for governor and thought the job was too small,” said one longtime Democratic strategist. “He is like many other people who have significant wealth and are looking at the person in the White House and thinking, ‘Heck, I’d be better than he would.’ I don’t think he’s unique in that. But he has been active longer and doing it more creatively than many of these people.”

Even if it is all being done to further the interest of one Steyer, Tom, Democrats elsewhere may stand to benefit too.

Money for Need to Impeach comes directly from Steyer, making it difficult to track exactly how much he’s spending on the effort. But his foremost political vehicle, NextGen Climate Action, has raised more than $16 million during the 2018 election cycle. And more than half of those funds have been passed along to other groups or spent on political activity in support of specific candidates.

Foremost among the latter was Virginia Gov. Ralph Northam, for whom NextGen provided more than $765,000 in in-kind goods and services during his run last year. (It was not lost on Virginia operatives that on the night of Northam’s win, Steyer was doing cable appearances from the victory party.)

The group has donated millions more to leading left-wing political organizations, including prominent Democratic groups such as opposition research group American Bridge 21st Century, labor union-backed super PAC for Our Future, and, most recently, a $1.5 million contribution to a new state-level political outfit called State Victory Action.

Some of NextGen’s financial and in-kind contributions are of particular note given the states to which they’ve been directed. Virginia Democrats—including Northam, Attorney General Mark Herring, and Lieutenant Governor Justin Fairfax—have been prominent beneficiaries. The group has also donated to Democrat-aligned organizations in Nevada, Ohio, and Florida, all states with competitive 2018 Senate races, and all key presidential swing states. NextGen Rising, the youth turnout entity housed in one of Steyer’s nonprofit groups, has been highly active in 10 states, including the crucial battlegrounds of Florida, Nevada, Wisconsin, Michigan, Iowa, Pennsylvania, New Hampshire, and Virginia.

Need to Impeach is turning toward campaign organizing as well. Mack said the group conducted voter turnout efforts during the special election in Pennsylvania’s 18th district, where it had 4,800 people on its email list. They plan to distribute tool kits for voter registration and turnout to those members in competitive congressional districts as November nears.

Recently, Steyer has begun holding town halls on impeachment—an effort pitched as a way to gin up grassroots support but one seen by operatives as a campaign-training exercise for its benefactor. “It’s like a boxer getting a sparring partner” is how Devine put it.

As Steyer’s profile has grown, so too has the wariness among a faction of Democrats. Lawmakers on the Hill who support impeachment say they’re frustrated by how little interest Steyer seems to have in their legislative efforts.

“It’s a good message, but if you’re trying to be effective, mention there is a bill and urge representatives to get on that bill,” said one Democratic House member, who nevertheless conceded that Steyer had been helpful in raising the profile of the issue.

And party leadership, including House Minority Leader and fellow San Franciscan Nancy Pelosi, have made their discomfort with the topic abundantly clear. Steyer, who didn’t consult Pelosi before launching his Need to Impeach campaign, seems to be taking the criticism in stride, more than content to be at the vanguard of the party’s digital operations and its resistance movement.

“Frustrating members of Congress is not really our concern. It’s our job to shine a light on the problem, and their job to fix it,” said Mack. “Tom is giving voice to the American people who want to take action. They have an affinity for him and what he is doing.”