It’s all fueling speculation that Hogan, a 62-year-old cancer survivor who coasted to reelection in liberal Maryland and remains one of the most popular governors in the country, is open to the prospect of a long-shot primary challenge to the incumbent president. His flirtation comes at a time when Trump is facing increasing blowback over his handling of the protracted government shutdown and bracing for a potentially devastating report by special counsel Robert Mueller.

Hogan used his inaugural address on Wednesday to repudiate the “debilitating politics” of Washington — and to raise the specter of impeachment. He recalled how his father, former Rep. Lawrence Hogan, was the first Republican congressman to support the removal of Richard Nixon.

The governor didn’t utter Trump’s name, but the implication was clear.

“Despite tremendous political pressure, he put aside partisanship and answered the demands of his conscience to do what he thought was the right thing for the nation that he loved,” Hogan said of his late father.

The White House is paying close attention. The president’s political aides have been monitoring the Maryland governor for months, and several said they regarded the inauguration speech as an unmistakable act of aggression. They noted that Trump 2016 primary rival Jeb Bush was a featured speaker at the ceremony, and that Mark Salter, a longtime Republican speechwriter and a fierce Trump critic, helped craft Hogan’s address.

“Any potential challenger should understand that the Trump campaign is better organized than any campaign in history, especially with the support of the Republican Party, which is firmly behind the president,” said Chris Carr, the Trump 2020 political director.

Hogan aides strenuously deny that he’s actively exploring a White House bid and point out that he’s stressed the themes of above-the-fray moderation and bipartisanship throughout his tenure.

Yet he’s given hope to Never Trump Republicans like Bill Kristol, a high-profile conservative commentator who’s been waging a Hail Mary campaign to stop the president from being renominated in 2020.

Kristol was invited to Hogan’s inauguration — though he didn’t attend — and he’s expected to meet soon with the governor. Kristol and Hogan briefly chatted last month after the Maryland Republican delivered a speech at the Niskanen Center, a right-of-center think tank that’s been critical of the president.

“He went out of his way to be a little more forward-leaning than he needed to be. He could have given a very good inaugural speech for his second term as governor without the father, without the impeachment, without the contrast with Washington, so he knows what he’s doing,” Kristol said.

“He’s a savvy pol,” Kristol added. “He wanted people to see that he had some interest in the national scene.”

The speech doesn’t necessarily mean he’s preparing to run, Kristol said. But Hogan has at least opened the door, Kristol argued, just as Utah Sen. Mitt Romney did with his recent op-ed declaring that Trump hadn’t “risen to the mantle” of the presidency.

Hogan’s upcoming trip to Iowa in March will likely only stoke the speculation. Though people involved insist the location is a coincidence — Hogan was originally planning to participate in an earlier NGA event in Las Vegas but canceled to attend George H.W. Bush’s funeral — his presence in the first-in-the-nation caucus state won’t go unnoticed.

Hogan is also expected to use his leadership of the NGA to raise his media profile. He’s slated to appear in an upcoming PBS special about governors and also to attend the Alfafa Club’s annual black-tie dinner, an exclusive affair that draws the Washington elite. Last week, Hogan co-wrote a letter to Trump and congressional leaders of both parties calling the shutdown a “failure in governance” and urging them to reach a compromise.

The governor is mostly playing coy about his intentions.

Last week, he hosted a handful of Niskanen Center officials for lunch ahead of his swearing-in. The discussion focused largely on policy matters, but Hogan, who’ll be termed out of office in 2022, was asked about his interest in launching a presidential bid. He did not rule out the possibility, one person familiar with the gathering said.

Similarly, when POLITICO asked Hogan in November about a potential 2020 campaign, the governor responded: “Never say never.”

Trump, meanwhile, is tightening his grip on the GOP apparatus with the explicit intention of snuffing out any vestiges of GOP opposition. In an unprecedented arrangement, the president’s reelection campaign has formally linked up with the Republican National Committee. And Trump political aides have launched a far-reaching effort to ensure that delegates to the 2020 GOP convention are presidential loyalists, not Never Trump Republicans looking to create a circus.

The RNC is expected to consider a resolution at its annual winter meeting in New Mexico next week declaring that Trump has the committee’s undivided support.

With Trump ensconced in the White House, many of the Republicans who vigorously opposed him in 2016 say they have no interest in standing in his way this time around. Craig Duchossois, a Chicago investor who helped to finance an anti-Trump super PAC in 2016, said he’d ruled out funding a similar effort in 2020.

“Not a shot,” Duchossois said.

Still, a small cadre of Republican donors, activists and operatives remain intent on stopping Trump. While they concede that preventing the president from winning renomination would be exceedingly difficult, they insist that primary voters will be willing to consider other candidates — especially if Trump’s legal challenges intensify.

The Never Trump Republicans have begun assembling a roster of would-be challengers, though there’s no consensus pick. Among the names on their wish list are Nebraska Sen. Ben Sasse, former Sens. Jeff Flake and Bob Corker, and former Ambassador to the U.N. Nikki Haley. Others are holding out hope for Jim Mattis, the just-resigned secretary of defense whom anti-Trump activists failed to recruit in a last-ditch 2016 effort to stop Trump’s nomination.

Former Ohio Gov. John Kasich is actively contemplating a 2020 campaign. This week, he flew to California to meet with potential donors and gauge their interest.

Some of the remaining Trump holdouts found hope in Romney’s op-ed earlier this month ripping Trump, saying it suggested the new senator might be open to challenging the president. Romney has said he won’t challenge Trump, though he’s so far refused to endorse the president’s reelection bid.

“I’m willing to look at alternatives to Trump. I will not support Donald Trump or Mike Pence in any way,” said Bill Kunkler, a Chicago private equity investor and major GOP donor who contributed over $350,000 to a super PAC that backed Romney’s 2012 presidential bid. “As a Republican, I’m ashamed of what I see.”

Others are pining for Hogan.

At his December speech before the Niskanen Center, Hogan was introduced by Jerry Taylor, the organization’s president. As he took the stage, Taylor handed the governor a gift: a book about the history of New Hampshire.