The U.S. Constitution makes President Donald Trump the commander in chief. The responsibility of raising and maintaining a military, however, was assigned by our Founding Fathers to Congress.

From the administrations of Lincoln and Wilson to FDR and Reagan, every serious defense buildup has required bipartisan support from the House and Senate. Today, America's armed forces need another jolt.

So, once again, members of Congress must play their part to make sure our military can deliver enough punch to protect our homeland and our vital interests abroad.

The global forces of instability are growing, especially in three parts of the world where regional peace and stability are particularly important to the U.S.

The solidity of Europe, Asia and the Middle East is threatened by Russia, China, Iran, North Korea and the transnational Islamist threat spearheaded by al-Qaida and the Islamic State.

Individually, none of these powers rise to the level of menace posed by the old Soviet Union. But when one of these threats acts up, we cannot expect the others to stand down. Indeed, we can expect them to try to exploit the situation.

For that reason, the U.S. must have the capacity to deal with all of them at once, and here we have a problem. While we need to be able to respond globally, the Pentagon no longer has a global-size force.

The Heritage Foundation's annual Index of U.S. Military Strength objectively measures the ability of our armed forces to protect vital national interests in a multi-conflict scenario.

And the measurement shows that, in terms of capacity, capability and readiness, the military has been in noticeable decline for years. In the 2017 index, the military's overall ability to provide the hard power needed to prevail in a multi-conflict scenario was rated as "marginal." Subsequent assessments suggest no change in the downward trend.

There are several reasons for the deteriorating assessments. Our competitors have become more aggressive and significantly beefed up their military capabilities.

Meanwhile, our allies - particularly those in Europe - have woefully under-invested in defense. But the biggest factor has been our own failure to reinvest in our increasingly strained military. The defense budget has been cut by 25 percent over the last five years.

U.S. combat operations have declined since the Bush era, but contrary to President Obama's claims, no wars have been ended.

Meanwhile, other operational demands, such as increased deployments to Western Europe, have arisen.

Yet our military is markedly smaller than it was a decade ago. In fact, the Army is smaller than at any time since before World War II. The Navy and Air Force are likewise at historically small levels.

Readiness is another problem. Top brass have testified that only three of 58 Army brigade combat teams are ready to fight; less than half of the Air Force is ready, and half of the Navy's aircraft are grounded for parts or maintenance.

And budget cuts have dramatically reduced flight hours for pilots and other training essential to keeping our warriors sharp and safe.

President Trump has proposed boosting the Pentagon's budget, but his proposal is at least $30 billion short of what it needs to be. Far greater investment will be needed if we want to assure that America can remain a global power.