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Fact check: Trump constructs false, misleading claims about his border 'wall'

Trump repeated one false claim — that the wall is already under construction — at least eight times in one day.

President Donald Trump put his long-promised border wall at the center of the government funding debate on Tuesday, repeating the frequently fact-checked falsehood that it's already under construction no fewer than eight times while making a host of questionable new assertions.

Here are Trump's claims, made on Twitter and during a testy public spat with Democratic leaders at the White House, and the facts. The White House did not respond to a request for more clarity.

1. We're building the border wall.

"Tremendous amounts of wall have already been built, and a lot of — a lot of wall," Trump said in the Oval Office. "In San Diego, we’re building new walls right now."

This is still false. The government is currently repairing and replacing old sections of border fencing, but construction on a new section of border barrier has not yet begun and won't this year.

2. A lot of the wall is already "built."

"But the wall will get built. A lot of the wall is built. It's been very effective," Trump said at the White House.

This is misleading at best, given that no new sections of border fencing have actually been built under Trump. The president seems to be referring to the 650 miles of existing fencing or barrier along the southern border, the majority of which was constructed long before he launched his bid for president, as "the wall." Under his administration, old fencing has been repaired and replaced.

It's unclear when these existing fences became an accepted part of his vision for "the wall," since he repeatedly derided fencing on the 2016 campaign trail in favor of a concrete barrier that would run the 2,000 mile stretch of the U.S.-Mexico border.

3. Existing border wall sections have caused "illegal traffic" to decline.

"If you look at San Diego, illegal traffic dropped 92 percent once the wall was up," Trump said in the Oval Office, listing off similar numbers for what he said were border wall sections in El Paso, Texas, Tuscon, Arizona, and Yuma, Arizona.

Trump's numbers need context, in part because Trump is referring to sections of the U.S.-Mexico border that are secured by the fencing he derided on the campaign trail and built long before his administration.

Border fencing was installed in San Diego in 1992, and the Department of Homeland Security said that total apprehensions fell 92 percent over the following 23 years.

DHS declined to offer any source data here, but the entire southern border has seen significantly fewer crossings than it did decades ago. In 2000, there were approximately 1.67 million apprehensions; in 2017, there were approximately 310,000.

4. Migrants bring disease.

"People with tremendous medical difficulties and medical problems are pouring in," Trump said in the Oval Office, echoing an earlier tweet that suggests migrants bring disease.

There's no evidence of this, according to a new report released last week. A group of 24 medical experts spent two years analyzing whether migration spreads disease, as well as looking into the effects that migrants have on health in their new homelands. Their conclusion: Immigrants make up a significant portion of the health care workforce, and migration boosts economies overall.

"There is no evidence to show that migrants are spreading disease," said Dr. Paul Spiegel, one of the experts who worked on the study who directs the Center for Humanitarian Health at Johns Hopkins School of Public Health. "That is a false argument that is used to keep migrants out," Spiegel told NBC News.

5. Ten terrorists were just caught by border authorities.

"We caught 10 terrorists over the last very short period of time. Ten. These are very serious people. Our border agents, all of our law enforcement has been incredible what they've done. But we caught 10 terrorists. These are people that were looking to do harm," Trump said in the Oval Office.

There's no public evidence that border authorities foiled ten terrorists recently. The White House, FBI, and DHS all either did not respond to comment or did not offer information about which ten terrorists were caught to back up Trump's claim.

However, DHS data does say the agency prevents an average of 10 suspected terrorists — identified on terror watch lists — from entering the U.S. each day.

6. The military could build the border wall.

"Yes, if we don't get what we want, one way or the other — whether it's through you, through a military, through anything you want to call — I will shut down the government," Trump told Senate Minority Leader Chuck Schumer, D-N.Y., and House Speaker-designate Nancy Pelosi of the proposed border wall.

This is true, under certain circumstances, according to the Pentagon.

"To date, there is no plan to build sections of the wall. However, Congress has provided options under Title 10 U.S. Code that could permit the Department of Defense to fund border barrier projects, such as in support of counter drug operations or national emergencies," Defense Department spokesman Jamie Davis said in a statement on Tuesday.