Donald Trump has declared a national emergency in an effort to secure resources to build a wall on the US-Mexico border.

Here are key questions answered on what this means:

What is a national emergency?

A president can declare a national emergency under the 1976 National Emergencies Act, which was passed in the aftermath of the Watergate crisis in an attempt to limit, not expand, executive power. The act does not define what constitutes a “national emergency.” But it does require the White House to put forward a legal justification for any emergency declaration and requires a congressional review every six months.

Presidents have declared 59 national emergencies since the law went into effect, according to the Brennan Center for Justice.

Separate laws govern various emergency powers that a president might invoke, from deploying troops inside the United States to restricting electronic communications. Trump reportedly wants to activate emergency military construction under a 1980s-era law that explicitly awards the defense department such power in the event of a national emergency declared by the president “that requires use of the armed forces.”

Is this a big deal?

The analysis flies in both directions on this question. Some legal experts say the emergency declaration is deeply alarming because it represents an aggressive power-grab by the president on funding issues. The constitution allots the power of the purse uniquely to Congress. Here, Congress has refused to pay for Trump’s border wall, and now it appears that Trump is trying to usurp the appropriations power.

But it might not be a big deal?

Many legal analysts take a more sanguine attitude about the emergency declaration. They point out that any declaration built on shaky legal ground is likely to collapse in court. They point out that Democratic House speaker Nancy Pelosi has the power to force the Republican-controlled Senate to vote on a resolution to rescind the declaration. If that fails, it could extract a potentially large political cost from Republicans.

Finally, voices counseling calm in the face of the emergency declaration point to the 59 emergency declarations made by presidents since the 1976 National Emergencies Act. It emerges that presidents declare national emergencies with fair regularity. The most recent such declaration, in November of last year, is described as blocking the “property of certain persons contributing to the situation in Nicaragua”.

Will the ‘emergency’ get Trump his wall?

In theory it could. Following the declaration of a national emergency, military officials are empowered to divert funding and resources “essential to the national defense” including the “use of the armed forces”.

So Trump could order the military to move money and troops around to address the emergency – in this case, Trump imagines, by building a wall.

But many analysts believe that the emergency declaration will not produce a wall, owing to the aforementioned anticipated challenges in the courts and Congress. Or it will fail due to public outcry or perhaps to a breakdown in compliance somewhere in the chain of command, either on the part of military officials or Trump’s own legal team.

What are the political implications?

A CNN poll conducted 30 January through 2 February found that a strong majority of the public was opposed to the idea of Trump declaring a national emergency to build his wall. In response to the question, “Should Trump Declare Emergency to Build Wall?”, 31% said yes while 66% said no.

The national emergency declaration seems particularly to pose political hazards for Republicans in Congress. If they are forced to vote in support of the president, they risk being tied to a potentially unpopular policy and eroding their credentials as devotees to the US constitution, whose checks on the presidency were sermonized gospel among Republicans during the Barack Obama years.

But as bad as that could get for Republicans, Mitch McConnell might have decided that the political risks of a national emergency were smaller than those of a second government shutdown in 2019, which Trump had also threatened but many saw as a likely political disaster.