President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE on Saturday defended his decision to order thousands of active-duty troops to the nation's southern border amid increasing scrutiny from lawmakers demanding answers on the deployment.

Top military officials confirmed this week that no active-duty troops are likely to be added to the roughly 5,800 already at the U.S.-Mexico border. Trump said Saturday that the troops will be there "as long as necessary."

"They build great fencing, they built a very powerful fence,” Trump told reporters on the South Lawn of the White House before leaving for a trip to California on Saturday. “The fence is fully manned, nobody gets through."

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Members of both parties criticized Trump’s decision to send the troops to the border ahead of the Nov. 6 midterm elections. Trump argued the troops were necessary to bolster border enforcement amid an approaching migrant caravan.

But lawmakers argue that the shrinking caravan of several thousand Central American asylum-seekers is still weeks away from potentially arriving at the U.S. border, and there is no clear objective or cost estimate for troops deployed there.

“I think it’s unfortunate that we have the soldiers [at the border],” retiring Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeHow fast population growth made Arizona a swing state Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden MORE (R-Ariz.), a vocal critic of Trump, said Wednesday on MSNBC's "Morning Joe.”

“You can’t call it anything but a stunt here, and it’s unfortunate that they’re going to be away from family during the holidays coming up, and we just don’t know what really for," he added.

Trump at one point before the election this month threatened to send up to 15,000 service members to the border to meet what he called an "invasion” of dangerous individuals.

Many lawmakers noted that president said little in the days after the election about the border deployment or the caravan trekking toward the distant U.S. border, though he raised the issue in a pair of tweets on Friday.

The Pentagon had said that up to 7,000 troops would go in support of U.S. Customs and Border Protection (CBP), but Deputy Defense Secretary Patrick Shanahan said Thursday the number has “pretty much peaked” at around 5,800.

The current mission is scheduled to end Dec. 15, with the commander in charge of the mission planning to examine this coming week whether to begin sending forces home.

Rep. Adam Smith David (Adam) Adam SmithWhen 'Buy American' and common sense collide Overnight Defense: Marine Corps brushes off criticism of Marines' appearance in GOP convention video | US troops injured in collision with Russian vehicle in Syria | Dems ask for probe of Vindman retaliation allegations Democrats press Pentagon watchdog to probe allegations of retaliation against Vindman brothers MORE (D-Wash.), who is likely to be the incoming Democratic chairman of the House Armed Services Committee, has said Democrats will hold hearings in an attempt to get U.S. officials to explain their reasoning for the hasty deployment.

“We would ask the Pentagon to come in and explain to us in an open public hearing what they’re doing and why,” Smith told The Washington Post earlier this month. “I don’t think we should let the president get away with this type of policy with no justification and no explanation for it.”

More than 100 House Democrats also signed a letter to Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE earlier this month asking him to answer a number of questions on the mission, including its cost and duration.

Senate Armed Services Committee ranking member Sen. Jack Reed John (Jack) Francis ReedWhen 'Buy American' and common sense collide Hillicon Valley: Russia 'amplifying' concerns around mail-in voting to undermine election | Facebook and Twitter take steps to limit Trump remarks on voting | Facebook to block political ads ahead of election Top Democrats press Trump to sanction Russian individuals over 2020 election interference efforts MORE (D-R.I.), dismissed Trump's decision to send the active-duty troops to the border as "unwise, unproductive" and "politically motived."

"Your decision to rush thousands of our troops to the border at this time seems politically motivated and fails to implement reasonable and appropriate steps to address the true nature of the problem," Reed wrote earlier this month.

In addition, he criticized the administration for failing to provide indication to lawmakers that the migrant caravan poses a direct national security threat to the U.S.

As questions mounted this past week, multiple reports flooded in of active duty-troops restless and underutilized at the border.

Time Magazine, in an article released Thursday, reported on an Army company sent to a small Arizona border town to bolster the border fence in a mission they are not trained or equipped to do.

Army Capt. Charles Matthews told Time that with the details of the mission unclear, they hauled from Texas heavy equipment more routinely used in war zones in the Middle East. Those vehicles have largely sat useless.

”We made an assumption that we would be doing horizontal earthwork: improving roads, you know, something in our wheelhouse,” he said. “We came out here and found we were wrong.”

About 75 miles away at Davis-­Monthan Air Force Base in Tucson, Ariz., where most of the 1,500 troops deployed to the state are situated, soldiers routinely find themselves with not much to do, according to the article.

Mattis on Wednesday defended the deployment and told reporters “in terms of readiness, it’s actually, I believe, so far improving our readiness for deployments.”

Defense officials have not given a cost estimate for the deployment, and figures from outside organizations puts the amount somewhere between $42 million and $110 million. U.S. officials have put the cost at more than $220 million, according to Time.

Questions have also been raised over the usefulness or need of active-duty forces at the border, as the Posse Comitatus Act of 1878 forbids such troops in taking part in domestic law enforcement.

Mattis has so far dodged questions on cost and the specific national security threat at the border, and said the military’s mission is only to “back up” CBP.

Speaking to reporters this week en route to visit troops at the border in Texas, Mattis said that preliminary figures on the mission’s cost are “not anywhere near right.”

He added that “very quickly we’ll know the real cost. So we’ll keep you posted as the real costs come in.”

And asked whether he thinks there is a security threat at the border that justifies the use of the active-duty troops, Mattis deferred to Homeland Security Secretary Kirstjen Nielsen Kirstjen Michele NielsenMore than million in DHS contracts awarded to firm of acting secretary's wife: report DHS IG won't investigate after watchdog said Wolf, Cuccinelli appointments violated law Appeals court sides with Trump over drawdown of immigrant protections MORE.

“The eyes of the world right now — certainly all of the Americans — are on you,” Mattis told troops during the visit. He added that they are part of a “nontraditional” mission.

Asked by a soldier what the long-term plans were for the military mission, Mattis said it is “somewhat to be determined.”

Asked on MSNBC what he would tell troops wanting to know why there were deployed to the border, Flake emphasized that the move came at Trump's direction.

"I don’t know what I could tell them other than we shouldn’t be doing this, and this wasn’t an issue that Congress was involved in, it was an executive decision," he said.