Americans have legitimate reason to be concerned about North Korea's use of nuclear weapons. Experts say that within two years the Hermit Kingdom could field the kind of technology that would back up its leaders' blustery rhetoric, and while the Defense Department won't publicly confirm Pyongyang's offensive capabilities, military leaders aren't waiting to find out.

The concern is more relevant now than ever amid an unprecedented number of North Korean tests of nuclear weapons and the missiles that would carry them, combined with assurances from President Donald Trump, Vice President Mike Pence and others within their young administration that the era of tolerating Kim Jong Un's bellicose behavior is over.

North Korea reaffirmed its pledges against the U.S. as recently as Thursday, saying any military provocation would result in a "merciless just nuclear strike at them at once," according to an article in its state-sponsored Rodong Sinmun news service.

Such rhetoric has made a political solution with the erratic regime seem less than likely, leaving questions about what military options are in front of the Trump administration. Should the U.S. decide to act pre-emptively, it has basically two outcomes it could pursue: deter the regime from further aggressive behavior or cripple its capabilities.

Reports in recent days have suggested U.S. officials are considering shooting down North Korea's test missiles, perhaps from destroyers positioned off the country's coast. More directly, though also more improbable, the administration could opt to target North Korea's nuclear facilities for destruction, using massive munitions capable of penetrating heavily fortified bunkers and tunnels deep underground.

The capability exists to pursue either option.

Earlier this month, the Trump administration ordered 59 Tomahawk missiles fired at Syria from U.S. warships in an attempt to deter that country from further use of chemical weapons. And, days later, U.S. forces dropped a 21,000-pound bomb – America's largest non-nuclear explosive – to destroy a compound held by an Islamic State affiliate in Afghanistan. Many analysts believe the strikes were largely for the benefit of Pyongyang, signalling that, unlike Barack Obama, this president has no qualms about employing the military to send a message.

Given the possibility of escalation implicit in military action on the Korean peninsula, the White House has reportedly opted for more covert activities, centering on its ability to hack into the Pyongyang's missile program and digitally disrupt its production. Sabotaging one measurement on one schematic, for example, could cause an entire rocket to malfunction.

The New York Times reported in March that Trump inherited advanced cyber weapons the Obama administration had developed to target North Korean missiles. Advisers to the government who spoke with U.S. News confirmed these tools specifically target the supply chain for the missiles, creating undetectable defects that cause issues at launch. Human informants on the ground in North Korea are also able to help penetrate the country's rudimentary electrical system and hack the launch programs.

"Cyber is the insurance policy: Let's go and disrupt these programs from the counter-proliferation perspective to the best that we can," says a cybersecurity expert familiar with the priorities of the Trump White House, who spoke on the condition of anonymity. "It's a viable way to disrupt the capability development inside North Korea."

Yet that has limits, and experts warn against thinking there are any quick solutions to the complex problems of North Korea's weapons program.

"Cyber is not a magic wand that we can wave at this problem and make it go away," says Tom Karako, a senior fellow with the Center for Strategic and International Studies' Missile Defense Project.

The U.S. ability to penetrate into North Korea to determine, for example, whether a missile failure was the result of the U.S. degrading the manufacturing process or whether it was merely the result of incompetence "is pretty dim," Karako says.

That means the likelihood of offsetting an attack from Pyongyang centers on whether the U.S. can provide adequate and credible defenses.

And the threats North Korea poses are varied.

In propaganda videos and public statements, the regime claims it could attack America's West Coast with a nuclear-tipped intercontinental ballistic missile. One video from 2013 portrays its weapons reaching as far as the White House and U.S. Capitol.

While estimates of the size and potency of North Korea's arsenal vary widely, the country is believed to possess nuclear weapons. North Korean scientists have successfully conducted tests as recently as last year that resulted in a blast more powerful than was produced by the bomb the U.S. dropped on Hiroshima in 1945, but their ability to miniaturize the technology in order to affix it to a missile remains unclear.

The missiles North Korea has developed could be capable of carrying out its belligerent threats, particularly if its researchers have perfected the ability to tip them with nuclear weapons. The Taepodong-2 missile, for example, is considered operational and has a range as far as 9,300 miles, which could reach the state of Maine. But most experts agree the technology isn't reliable and question whether the rocket, developed for a civilian space program, could be effectively outfitted to accurately hit a target in the U.S. while carrying a warhead.

Still, the consensus is that the technology is within sight. Pyongyang has fielded Scud-like missiles capable of ranges from 180 to 300 miles, far enough to reach its southern neighbor or Japan, according to a Center for Strategic and International Studies report . Others in development could extend their reach.

The question is whether the U.S. can contain North Korea, either in preventing it from achieving nuclear ICBM technology or defending against an incoming attack were it to get to that level. To the latter end, no aspect of the U.S. intercontinental ballistic missile defense shield is considered 100 percent effective, largely because it's never operated in a real-world environment.

The U.S. Ground-based Midcourse Defense system, overseen by the Missile Defense Agency, or MDA, is considered one of the primary shields for the U.S. homeland against an incoming missile fired by a rogue regime like North Korea since its first successful missile intercept test in 1999. It consists of 36 interceptors deployed at military bases in Alaska and California.

The track record for this program, however, is less than encouraging – as of February, three of the last four tests have failed, MDA reports , and since testing began only nine of the 17 tests have succeeded. A military review conducted for fiscal 2016 concluded the system has "demonstrated a limited capability to defend the U.S. homeland from small numbers of simple intermediate-range or intercontinental ballistic missile threats launched from North Korea or Iran."

Pyongyang could also try to strike a U.S. target nearer its launchpads, like Hawaii, using ground-based weapons or mobile launched missiles believed to be operational, like the KN-08, which are harder to detect.

But America's missile defense extends beyond its shores. The Navy oversees the Aegis Ballistic Missile Defense system, deployed aboard 22 Navy cruisers and 62 destroyers – some of which are a part of a group of ships Trump said he would deploy to the Korean peninsula and which are now making their way. Those have a better test track record, according to MDA, but they are designed to take down short- and intermediate-range ballistic missiles with an estimated range of up to 3,400 miles, not intercontinental weapons.

In its immediate neighborhood, North Korea could launch attacks against South Korea or Japan – two countries that have military treaty alliances with the U.S. and are home to tens of thousands of U.S. forces stationed there.

At the front lines are mobile defenses, including the Terminal High Altitude Area Defense radar system the U.S. under the Trump administration deployed to South Korea after months of deliberations under Obama, and much to the consternation of the Chinese , who see the tracking system as a way to rein in their military might. The system is not expected to be operational until May at the earliest.

MDA boasts a perfect 13-out-of-13 record for THAAD missile tests, but its ability to provide real-world protection is also a question. Some experts fear Seoul's proximity to the North Korean border, a mere 25 miles from the heart of the capital, wouldn't give the THAAD system enough time to destroy incoming missiles before they strike a location at which 60 percent of South Korea's population resides.

The Pentagon is actively working to improve its missile defense capabilities and is planning exercises in California and Hawaii at the end of May to refine its systems, which are still comparable to firing one bullet at another bullet. The tests will simulate shooting down an intercontinental ballistic missile over the Pacific Ocean.