WASHINGTON – President Donald Trump has declared a national emergency to pay for his long-promised and controversial border wall.

The national emergency and other measures will free up $8 billion – far more than the $5.7 billion he initially demanded – to free up funding for 234 miles of bollard wall, the White House said. It's a move that is almost guaranteed to draw the White House into a lengthy legal battle over the president's ability to use the tool for that purpose.

So where will the White House find that money?

More:Candidate Trump said Mexico would pay for the wall. What happened?

Military construction

Trump will attempt to access $3.6 billion in military construction money. Unlike other portions of the plan, the president must declare a national emergency to access this account, which has long been rumored to be under consideration. The money is used for military bases and other projects. President George W. Bush tapped into this same account after he declared a national emergency following the 2001 terrorist attacks.

White House officials said they did not yet know which military constructions might be cancelled or delayed by the move.

Asset forfeiture

Trump will dip into about $600 million in asset forfeiture funds at Department of Treasury. This funding has been controversial on both sides of the aisle because it comes from government seizures of property.

More:National emergencies are common; declaring one for a border wall is not

More:Trump's emergency declaration would trigger a drawn-out legal fight

More:How congressional Democrats could fight a Trump national emergency

Drug interdiction

Current law gives the president power to rely on the Department of Defense for drug interdiction in certain cases, even without a national emergency. The law says the Pentagon can assist in that effort through the building of fences and other measures. The White House believes it can draw about $2.5 billion through this provision.

White House officials did not say, specifically, where that money will come from.

Congressional funding

Part of Trump's package includes the $1.375 billion that Congress approved on a bipartisan basis for border barriers late Thursday night. That measure, which will also avert another government shutdown, limits Trump to spending the money only on previously approved barrier designs, including the "bollard wall" design that was also used by the Obama administration.