First of all, Orange leader didn't "shut down the border" as you falsely claim.
For starters, health experts say Trump was wrong to refer to the travel restrictions as a “travel ban,” as he did in a telephone
interview on March 4 with Fox News’ Sean Hannity. During a
town hall on March 5, Trump said he “closed down the borders to China and to other areas that are very badly affected.” That’s not accurate.
As Azar explained when he
announced the travel restrictions on Jan. 31, the
policy prohibits non-U.S. citizens, other than the immediate family of U.S. citizens and permanent residents, who have traveled to China within the last two weeks from entering the U.S.
At a
House subcommittee hearing on the coronavirus on Feb. 5, Ron Klain, White House Ebola response coordinator under the Obama administration, took issue with the characterization of the travel restrictions as a travel “ban.”
“We don’t have a travel ban,” Klain said. “We have a travel Band-Aid right now.
First, before it was imposed, 300,000 people came here from China in the previous month. So, the horse is out of the barn.”
“There’s no restriction on Americans going back and forth,” Klain said. “There are warnings. People should abide by those warnings. But today, 30 planes will land in Los Angeles that either originated in Beijing or came here on one-stops, 30 in San Francisco, 25 in New York City. Okay? So, unless we think that the color of the passport someone carries is a meaningful public health restriction, we have not placed a meaningful public health restriction.
Furthermore, Klain said, the import of goods from China is exempt from the travel restrictions, “and, of course, the people who fly the planes and drive the boats that bring those goods from China. We couldn’t ban that activity. We vitally need that. Ninety percent of the antibiotics in this country come from China. All kinds of vital medical supplies … we will use to treat people. So, travel bans … that’s not what we’re imposing, that’s not what exists.”
https://www.factcheck.org/2020/03/the-facts-on-trumps-travel-restrictions/
Secondly, South Korea didn't close it's borders yet went from having the most infections outside China to now one of the lowest with under 10k and only 165 deaths (US: 188k, 4k deaths). Why? Because they started testing right away and quarantining those who were positive.