President Trump declared on Friday that he would consider using emergency powers to build a border wall if he can't get the project financed through Congress. But doing so would set a dangerous precedent.

In response to a question during a press conference, Trump insisted he didn't need congressional approval to build a wall.

"We could call a national emergency because of the security of our country, absolutely," Trump said. "We can do it. I haven't done it, I may do it. I may do it. But we can call a national emergency and build it very quickly."

He added, "But if we can do it through a negotiated process, we're giving that a shot."

The U.S. system places important checks on presidential power. Though it's true that generally executive power is at its strongest in cases involving national security, for the sake of the republic, it's important to be wary of overly broad invocations of "emergency." The wider the interpretation of "emergency," then the more decisions can be arbitrarily imposed on the country by a single leader, and there lies the road to authoritarianism.

Some conservatives may cheer on the idea of Trump using emergency powers to achieve their favored outcome, but if he were to go through with it, it would only be a matter of time before the next Democratic president uses expanded powers to advance a priority conservatives would find deeply objectionable.

Emergencies should be invoked in very limited cases, such as natural disasters, or if there's an actual armed invasion. Whatever the arguments in favor of building a border wall, it does not rise to that threshold.