It’s a widely known fact that North Korea’s nuclear arsenal is growing by the minute, as they have conducted several tests with nuclear bombs.

According to North Korea, they have conducted five tests: one each in 2006, 2009, and 2013; and two in 2016. The test in September of 2016, according to North Korea, was able to create an explosive yield of 10-30 kilotons. (One kiloton is equal to 1,000 tons of TNT).

If this information is 100 percent correct, then the September 2016 test was the strongest North Korea has had yet.

President Trump has stated his opinion clearly on North Korea, tweeting that he denies that North Korea is able to reach the U.S. with nuclear weapons. This tweet perhaps he doesn’t believe they have the technology to do so, but regardless, he is prepared to call for war. However, if the U.S. were to go to war, experts say the U.S. wouldn’t have many options to do so, according to bbc.com.

Is Trump wrong? Can North Korea reach the U.S. with nuclear weapons? Experts say that answer is no, that any efforts made by North Korea would end up failing, according to the BBC. What they also estimate, however, is that North Korea will gain the ability to do so in five to 10 years.

The U.S. Secretary of Defense James Mattis stated that any use of nuclear weapons by North Korea would be met with an effective and overwhelming response, according to the BBC.

Mattis also has plans to deploy a U.S. missile defense system in South Korea later this year. In fact, the U.S. has a large presence of its army in South Korea and Japan, with just about under 28,500 troops in South Korea. Trump has said before he wants the troops in South Korea and Japan to maintain their military presence. It’s clear that nobody in the U.S. is joking around when it comes to North Korea when it comes to their nuclear capability.

“Any attack on the United States, or our allies, will be defeated, and any use of nuclear weapons would be met with a response that would be effective and overwhelming,” Mattis said to the BBC.