Here's what gets lost in the fight: This wouldn't be the first time we ever built border barriers or beefed up security. There's already fencing along as much as 690 miles of the border between the U.S. and Mexico, and the number of border agents has almost tripled in the past two decades.

Why it matters: That still leaves more than half of the almost 2,000-mile border uncovered, and there are gaps and dilapidated fencing in the barriers that are in place. The fight that has shut down the government is basically about 234 miles of new border wall that President Trump wants, according to the Trump administration's latest request.

By the numbers: Less than half of the border between the U.S. and Mexico has man-made barriers, according to Reveal News.

Only 403 miles of fencing is intended to keep out pedestrians, while the rest just keeps out vehicles, according to a study by the Federation for American Immigration Reform, an immigration group that advocates for lowering immigration levels.

is intended to keep out pedestrians, while the rest just keeps out vehicles, according to a study by the Federation for American Immigration Reform, an immigration group that advocates for lowering immigration levels. For 36 miles, there is a second tier of pedestrian fencing.

there is a second tier of pedestrian fencing. And for 14 miles, there are three layers of fencing.

there are three layers of fencing. In October, the Department of Homeland Security unveiled the 2.5-mile-long, 30-foot-tall steel slatted barrier in Calexico, California, dubbing it the first completed border wall project — despite the fact that it just replaced existing fencing.

the Department of Homeland Security unveiled the 2.5-mile-long, 30-foot-tall steel slatted barrier in Calexico, California, dubbing it the first completed border wall project — despite the fact that it just replaced existing fencing. The border also runs through the rugged, mountainous terrain of Big Bend National Park for 118 miles. Many local government officials fear that a wall would negatively impact wildlife and look bad in the beautiful park, NPR has reported.

through the rugged, mountainous terrain of Big Bend National Park for 118 miles. Many local government officials fear that a wall would negatively impact wildlife and look bad in the beautiful park, NPR has reported. 62 miles of the border are part of the Tohono O'Odham Nation reservation in Arizona. The nation has historic ties to Mexico as well as current tribe members there, and they'd be further cut off from each other if a wall was built, according to USA Today.

Trump wants $5.7 billion to build new steel barriers along 234 miles of the southern border, according to the latest letter sent by the White House to Senate Appropriations Committee Chairman Richard Shelby earlier this month.

Details: The priority would be to build a barrier along 104 miles in the Rio Grande Valley, which is a popular crossing point and has few barriers, Vox's Dara Lind reported. Next, the administration would focus on putting up barriers in a 27-mile stretch in Yuma, Arizona; 14 miles in El Centro, California; and 55 miles in Laredo, Texas.

The priority would be to build a barrier along 104 miles in the Rio Grande Valley, which is a popular crossing point and has few barriers, Vox's Dara Lind reported. Next, the administration would focus on putting up barriers in a 27-mile stretch in Yuma, Arizona; 14 miles in El Centro, California; and 55 miles in Laredo, Texas. What to watch: The government would have to use its powers of eminent domain to take private land from Americans at the border to build the wall — something that would likely spark a flurry of legal battles. Around 100 Texans have already received letters from the government asking for access to their land to look at how and where a wall could be built, the Washington Post reported.

Background: Trump has often changed his mind about the wall, at one point pitching Republicans that it could be covered in solar panels, another time insisting that it be "see-through," claiming it would be "artistically designed steel slats," and then insisting that "an all concrete Wall was NEVER ABANDONED."

He's changed his budget requests from $25 billion to $18 billion to $5 billion over the past year. But DHS only asked for $1.6 billion to build 65 miles worth of barriers in its 2019 budget request. The latest Trump administration proposal is an effort to expand that request.

The bottom line: Securing the rest of the border would be a huge challenge under the best political conditions. After the longest government shutdown in history, it's going to be even tougher.

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