WASHINGTON — Locked in a showdown with Congress over border wall funding, President Donald Trump moved the goalposts on Tuesday by suggesting that he would be satisfied with funding to renovate existing barrier — not just add barrier to parts of the border that aren't already fenced.

And he set a goal of 500 to 550 miles of barrier — new or replacement — in place by the 2020 election, 22 months away.

Prior to an unusual Christmas morning session with reporters in the Oval Office, on Day 4 of a partial government shutdown that hinges on his demand for wall funding, Trump had never publicly stated how many miles of barrier he wants.

This was also the first time he had said that replacing old fencing would count, in his mind, toward his central campaign promise of building a "big beautiful wall" on the U.S.-Mexico border.

"It's my hope to have this done, completed — all 500 to 550 miles — to have it either renovated or brand new by election time," he said Tuesday. He had spent the last week trying to soften opposition to the wall by describing it in new terms: as a "steel slat barrier" or even a "fence," a term and a design approach that he had long shunned as ineffective.

A partial government shutdown began at midnight on Friday.

Trump postponed a 17-day vacation at his Mar-a-Lago resort in Palm Beach, Fla. Congress is in recess until Thursday, the earliest possible day for the shutdown to end. Unless Trump backs down on his demand for $5 billion, or Senate Democrats cave into that demand, the shutdown will likely continue into January.

I am all alone (poor me) in the White House waiting for the Democrats to come back and make a deal on desperately needed Border Security. At some point the Democrats not wanting to make a deal will cost our Country more money than the Border Wall we are all talking about. Crazy! — Donald J. Trump (@realDonaldTrump) December 24, 2018

"I can't tell you when the government is going to reopen," Trump said in the Oval Office. "[Not until] we have a wall, a fence, whatever they'd like to call it. I'll call it whatever they want. But it's all the same thing. It's a barrier from people pouring into our country. ... It's a barrier from drugs. There is a problem in this world today called human trafficking. ... We are not going to let that take place. We are working so hard to catch these traffickers. They are bad people. We can't do it without a barrier, we can't do it without a wall."

Trump had invited the small media pool on duty to witness traditional Christmas Day calls to troops from the commander in chief, then took questions for nine minutes.

He indicated that he may be willing to budge from his $5 billion demand.

"It's complicated," he said, noting that Congress had authorized $25 billion for homeland security, though not for the wall. "We want the wall money to be increased."

Homeland Security Department officials said on Friday, hours before the shutdown, that $5 billion would be enough for 215 miles of barrier, of which about 100 miles would be along parts of the border that don't already have fencing. The rest would be replacement barrier — higher and harder to overcome than existing fences for migrants and drug smugglers.

Ahead of the shutdown, Trump initially agreed to a stopgap spending measure that lacked any funding for a wall. Under pressure from conservative media personalities, he shifted his stance and dug in, vowing to veto any measure that didn't include $5 billion for a wall.

With Republicans poised to lose control of the House on Jan. 3, any leverage he has will quickly disappear.

Earlier this year, Trump asked Congress for $18 billion, which the administration said was enough for about 700 miles of barrier.

Some — maybe most — would replace 654 miles of aging fence built under a 2006 law.

The border is nearly 2,000 miles long. The Rio Grande comprises much of that. Trump's latest demands suggest that even if he gets everything he wants, the majority of the border would remain unfenced.

That's a far cry from his oft-repeated campaign promise of a vast wall that Mexico would pay for. There is no proposal from the administration for Mexico to provide any funding, and Mexican officials have emphatically rejected the idea.