As President Donald Trump publicly weighs declaring a national emergency as a way to get his border wall, some Republicans are expressing concern about the precedent such a move could set for future — and Democratic — presidents.

Trump appears increasingly inclined to go the route of a national emergency to divert funds to a wall at the US-Mexico border as the partial government shutdown reaches its 21st day on Friday.

“If we don’t make a deal with Congress, most likely I will do that,” Trump told Fox News host Sean Hannity in a Thursday interview. “I would actually say I would. I can’t imagine any reason why not, because I’m allowed to do it. The law is 100 percent on my side.”

While declaring a national emergency is within his powers as president, some on the right are sounding alarms that Trump doing so in this circumstance would set the stage for future presidents to do the same. And not over immigration, but instead over issues like climate change, health care, or other Democratic Party priorities if and when a member of that party lands in the White House.

Sen. Marco Rubio (R-FL) said in an interview on CNBC’s Squawk Box on Thursday that he wasn’t “prepared to endorse” Trump’s use of a national emergency at the moment and warned of future fallout.

“It sets long-term precedents, and I can tell you, for people on my side of the aisle, one of the concerns we should have is if today the national emergency is border security and it entitles him to go out and do something, we all support that. Tomorrow, the national security emergency might be, you know, climate change, so let’s seize fossil fuel plants or something,” he said. “Maybe it’s an exaggeration, but my point is, we’ve got to be very careful about endorsing broad uses of executive power in our republic.”

Sen. Marco Rubio said he's not ready to support Trump declaring a national emergency over border security because under a Democratic president, "the national security emergency might be climate change." pic.twitter.com/2taNpiW5Nr — Rebecca Harrington (@HarringtonBecca) January 10, 2019

Rep. Matt Gaetz (R-FL) made a slippery slope argument against it in an interview with the Wall Street Journal. “I don’t want the next national emergency to be that some Democrat president says we have to build transgender bathrooms in every elementary school in America,” he said.

The Wall Street Journal’s editorial board issued a warning on Thursday, arguing that while the courts could potentially step in on Trump’s emergency declaration, there’s no guarantee that would happen.

“If Mr. Trump did win in court, a President Elizabeth Warren might take the precedent as a license to circumvent Congress whenever it is political expedient,” the editorial board wrote. “Rising carbon emissions or even income inequality could be declared national emergencies.”

Even Fox News has cautioned against a national emergency declaration. Fox & Friends host Brian Kilmeade on Thursday said it would “be a disaster in the big picture, and it would show us at being inept and unable to govern around the world.” He added that it would set a “terrible precedent.”

Republicans complained about overreach from Obama. Not doing it on Trump is a bad look.

Republicans for years publicly fretted about Barack Obama’s potential for presidential overreach. Now Trump is weighing declaring a national emergency — even though there isn’t one — and they’re kind of stuck. They want to back the president. They also don’t want to look bad, or set up a scenario where future presidents use a similar play.

Vox’s Jane Coaston recently explained Republican concerns:

Among conservatives, including those who are strongly in support of a border wall, the debate over a potential national emergency declaration was less about whether a wall in the style Trump promised time and again during the campaign is necessary than about the powers a president has, and should have.

“Do we really want to establish the precedent that the president can simply declare ‘It’s an emergency’ like some magical incantation and then completely bypass property rights and the will of Congress just so he can fulfill a campaign promise that, if Sam Nunberg is to be believed, began as a consultant’s gimmick to get the candidate Trump to talk about immigration and what a great builder he is?” Jonah Goldberg, a columnist at conservative publication the National Review, wrote on Monday.

“If President Trump begins to imitate Barack Obama in issuing dubious executive orders and trampling on private property rights, he could find himself in trouble even with portions of his base,” John Fund wrote separately in the National Review last weekend.

Democrats thus far appear pretty resistant to the idea of Trump declaring a national emergency and have decried his threats that he might do so. Some, however, have at least jumped onto the idea in jest.

“Pumped for the next Democratic president to use ‘emergency powers,’” Jon Favreau, a former Obama speechwriter and Crooked Media co-founder joked on Twitter on Thursday, envisioning a future just like the ones Republicans are scared of.

Pumped for the next Democratic president to use “emergency powers” for a Green New Deal (climate emergency), Medicare for All (public health emergency), and a new Voting Rights Act (democracy emergency)! https://t.co/cuC19W6nkH — Jon Favreau (@jonfavs) January 10, 2019

If Trump were to declare a national emergency to get the border wall, the move would certainly be scrutinized and likely subject to legal challenge in court. Congress could also overturn it with a two-thirds majority in both chambers, and it’s unclear how that would play out.

But Trump could at the very least make the first move: Under the National Emergencies Act of 1976, the president can issue an emergency declaration and draw from some 130 laws already codified by Congress to try to build the wall. His legal team is already figuring out ways to do it.