A lot of conservatives who can usually be counted on to invoke the Constitution can't stand Rand right now. That would be Sen. Rand Paul (R-Ky.), who broke with President Trump on using national emergency powers to fund border wall construction.

"Phony constitutionalist Rand Paul," tweeted popular radio talk show host Mark Levin. "Faux constitutionalism," concurred fellow commentator David Webb.

Paul says Trump is usurping Congress' constitutional spending powers by redirecting previously appropriated money toward the wall. These conservatives claim that isn't so — but some of their arguments sound awfully similar to the Democratic official who in 2012 celebrated a favorable ObamaCare ruling, squealing, "It's constitutional. Bitches."

That position may seem expedient now, but Paul is right on the Constitution and long-term political strategy alike.

To be sure, February wasn't a good month on the border. Illegal border crossings were at their highest total in 12 years, and arrests along the southern border are up 97 percent over last year. A majority of the apprehensions involve families and unaccompanied children, both of whom are harder to remove than single males and are often caught up in a broken asylum process. Physical barriers aren't a panacea, but they could help.

To many conservatives, this is good enough reason for Trump to act if Congress won't. But there are real constitutional questions raised by the executive branch invoking emergency powers on a policy question where lawmakers so recently rejected the president's plan. The situation is much like how the Senate had just specifically declined to pass the Dream Act before then-President Barack Obama created Deferred Action for Childhood Arrivals (DACA), later described by Trump as an "illegal executive amnesty."

Others point out that Trump is citing the 1976 National Emergencies Act in support of his decision, a law duly passed by Congress and signed by then-President Gerald Ford. That must make it constitutional, one correspondent told me.

If that's true, I'm not sure what the fuss about ObamaCare's constitutionality was all about. First, most of the previously declared emergencies don't involve spending money Congress explicitly decided to appropriate elsewhere. Second, it is by no means clear that Congress can transfer its constitutionally delegated powers to the executive branch by statute — or what the limiting principle would be.

Indeed, the leap from recognizing problems at the border to ignoring these constitutional concerns sounds troublingly familiar. Liberals are fond of arguing that anyone who objects to their proposed policy solution to a problem are against solving that problem. They can argue that many of their issues — health care, climate change, and gun violence, to name just a few — constitute dire emergencies. As Rep. Alexandria Ocasio-Cortez (D-N.Y.) told critics of her Green New Deal, "You try. You do it. Cuz you're not. Cuz you're not. So, until you do it, I'm the boss. How about that?"

An emergency declaration can't fund the Green New Deal in the way it can fund the border wall, constitutional questions aside. Trump is repurposing funds the federal government already has, while this proposal would require trillions of new dollars Washington currently lacks. But that won't stop liberals from declaring a lot of things are emergencies in the coming years, and conservatives' constitutional arguments will ring hollow if their handling of the border wall emergency today brands them as unprincipled, situational constitutionalists.

Moreover, if strict interpretation of the Constitution must go out the window anytime a problem is big enough, that assumption will benefit liberals far more often than conservatives. And what Trump can do today, a President Bernie Sanders, Elizabeth Warren, or — years from now — Ocasio-Cortez can do later. It is easy to imagine a post-Trump Democratic president doing a similar end-run around a Republican Congress to fund Planned Parenthood or continue DACA without legislative authorization.

That doesn't mean the problems at the border don't require a solution. But if conservatives want to continue making the case for constitutionally limited government at a time when the progressive agenda is replete with calls for expanded government services, they cannot endorse this emergency declaration. They must not behave under Trump in a way that makes anti-statist arguments appear opportunistic or in bad faith.

The Republican electorate has already moved rapidly in recent years from the exacting fiscal conservatism of the Tea Party under Obama to a more relaxed attitude about government spending, deficits, and debt under Trump. That shift severely damages any future GOP calls for fiscal responsibility, and a similar shift on constitutional authority will have similarly counterproductive consequences long-term.

As Democrats gain power and clamor for expanded government, constitutional conservatives will likely experience a revival of public support, much as they did early in the presidencies of Obama and Bill Clinton. If they want their arguments against untrammeled executive power taken seriously, they must start laying the groundwork now.