President Donald Trump will make his case to Americans on Tuesday that a “crisis” at the U.S. border with Mexico requires a wall in a prime-time address aimed at building support for a campaign promise that has sparked an 18-day government shutdown.

Trump’s Oval Office remarks, scheduled for 9 p.m. will be the president’s latest attempt to convince Democrats, not to mention furloughed government workers, to support his push for a steel barrier on the U.S. southern border that he says is needed to curb the flow of drugs and illegal immigration.

All the major U.S. television networks agreed to air Trump’s speech, prompting Democrats, who say a wall would be expensive, inefficient and immoral, to seek equal time.

Vice President Mike Pence, in a round of television interviews this morning, said Trump would use his address to explain to the American people that there is “a humanitarian and security crisis” at the southern U.S. border.

The emphasis on a crisis comes as Trump considers declaring a national emergency in an effort to bypass Congress and build the wall without its approval. The White House has not said what about the situation makes it a national emergency.

Democrats, who control the U.S. House of Representatives, have rejected Trump’s demand for $5.7 billion to help build such a wall. Talks to fund the government have broken down over that point, leaving several government agencies shuttered and some 800,000 government workers furloughed or working without pay.

Trump promised a wall as a candidate for the White House in 2016, making it one of his signature campaign issues and saying Mexico would pay for it. In December, he said he would be “proud” to shut the government down over the issue but has since blamed Democrats. Last week, he said the shutdown could last for months or even years.

Trump will continue pressing his case with a trip to the U.S. southern border on Thursday.