WASHINGTON (Reuters) - A partial shutdown of the federal government entered its 18th day on Tuesday as U.S. President Donald Trump prepared to make a nationally televised address to promote construction of his long-promised wall along the border with Mexico.

The dome of the U.S. Capitol is seen beyond a chain fence during the partial government shutdown in Washington, U.S., January 8, 2019. REUTERS/Kevin Lamarque

Trump, when he ran for president in 2016, said Mexico would pay for the barrier along the nation’s southern border. The Mexican government has steadfastly refused, causing Trump to demand payment from a Congress that also has balked.

As a result, Trump has refused to support legislation funding about one-quarter of government activities unless lawmakers provide $5.7 billion for a project that eventually could cost well over $23 billion.

Democrats, who control the U.S. House of Representatives, have called on Trump to reopen the government while talks continue on the wall. Senate Majority Leader Mitch McConnell has insisted that he will not bring any government funding bill up for a vote if Trump opposes it, although some of his fellow Republicans are tiring of the prolonged standoff.

The following are some key dates:

JAN. 8

Vice President Mike Pence speaks to congressional Republicans at the U.S. Capitol at 5:30 p.m. EST (2230 GMT).

Trump makes televised speech from the Oval Office about the border wall at 9 p.m. EST (0200 GMT Wednesday).

Some Democratic lawmakers plan an afternoon protest in front of the White House at Lafayette Park in Washington.

JAN. 9

House Democrats plan to begin approving individual bills to restore funding to federal agencies affected by the shutdown, without any wall funding. If passed, the bills would then go one-by-one to the Republican-controlled Senate, which is not expected to consider them, unless public pressure for action builds to higher levels.

JAN. 10

Trump travels to the U.S.-Mexico border to pitch for the wall.

Federal workers affected by the shutdown plan to rally in near the White House, the National Federation of Federal Employees union said.

JAN. 11

If still underway, the shutdown will be tied for the longest in recent history. In late 1995 and early 1996, under Democratic President Bill Clinton, federal agencies were shuttered for 21 days as he tangled with Republicans over budget matters.

JAN. 21-25

Congress is scheduled to leave Washington for a week for the Martin Luther King Jr. holiday.

JAN. 29

Trump is scheduled to deliver his annual State of the Union address to Congress.