HOUSTON — President Trump had considered declaring a national emergency to build the wall but stopped short of doing so Tuesday night.

If it happens, how would that national emergency declaration work?

We've seen a lot of talk about President Trump using his emergency powers to fulfill his campaign promise of building a border wall.

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We went to University of Houston Assistant Professor Emily Berman to get some answers on how this would work and what the consequences could be.

Here's what the law says.

“It does not have a definition of what constitutes a national emergency and so arguably, that determination is entirely up to the president's discretion," Berman said.

Different laws would allow the president to pull money from different places, but then the battle against it would most likely begin.

Berman says pushback could happen in three main ways.

Legislatively – it could mean hearings and bills to pull funding.

Judicially – lawsuits could be filed saying it's not what the law intended, or it goes against what Congress wants and then a judge could rule it unlawful.

Less commonly, she says there could be pushback within the executive branch itself with insiders using stalling tactics to weaken the project.

“And then, which one is going to be the effective one, will sort of shake out depending on how the politics will play out over the next several days and weeks,” Berman said.