United States President Donald Trump has pledged not to bend in his demand for a wall along the southern border with Mexico, but says the barrier could be made of steel instead of concrete as a potential compromise with Democrats who are refusing to fund the project.
Trump's address will air at 9 p.m.
Democrats have also requested time on the networks to respond to the president's remarks. Now Democratic leadership including House speaker Nancy Pelosi and Senate minority leader Chuck Schumer are demanding that the networks follow Trump's address with a rebuttal by Democrats.
The dispute over wall funding - Trump is demanding $5.7 billion USA to help build it - led to a stalemate in Congress over funding for parts of the government.
Trump also plans a personal visit to the Mexican border on Thursday as he tries to put pressure on newly empowered Democrats in the shutdown standoff.
Floodlights from the United States illuminate multiple border walls on January 7, 2019, as seen from Tijuana, Mexico.
President Donald Trump thought other presidents would back him over the wall.
Alabama fans blame 'Drake curse' for national championship loss to Clemson
Clemson hit Alabama with a 31-point first half, capitalizing on the Tide's mistakes and unleashing Lawrence's rocket arm. But we are, and I am! That led to Travis Etienne's third touchdown of the half, a 5-yard shovel pass from Lawrence.
The number of illegal border crossings is down from 1.6 million in 2000 to less than 400,000 a year ago. It invited representatives from cable news outlets to a White House lunch with Trump ahead of the address, a gesture that is typically reserved for the lead-up to State of the Union speeches.
The White House has not said why the situation constitutes a national emergency.
"If you listen carefully, you can hear network execs coming up with tortured, wholly unbelievable reasons for why they will air Trump's speech tomorrow night when they deemed one from Obama too political and refused to carry", tweeted Democratic political strategist Adam Parkhomenko.
"The president was asked whether it [the national emergency option] is something he was considering, and he said it is something we are looking at...."
Democrats have said they support increased border security measures such as additional USA border agents and technology, but have rejected the administration's claims about the security risks at the border and have raised concerns that Trump will use his speech to present a false narrative.
A spokesperson for George W Bush said that he never discussed the border wall with Mr Trump.
"The president has no authority to usurp Congress's power of the purse", House Judiciary Committee Chairman Jerrold Nadler, a Democrat from NY, said during a visit to the border on Monday. The shutdown, which has left some 800,000 government workers furloughed or working without pay, is also affecting national parks, airline security screening, housing and food aid, and economic data.
Len Saunders, an immigration lawyer based near the border in Blaine, Wash., said those border guards - many of whom are supportive of the president's border-security efforts - may soon stop showing up for work as they begin to feel the shutdown's financial impact. Two Guatemalan children have died in border custody, while images of border patrol officers firing tear gas at migrants have raised the ire of critics.