“If you’re not moving forward, you’re falling behind.” It’s a bromide, yes, but undeniably true when talking about the state of our nuclear weapons program.

In this area, America is falling further and further behind our competitors. It leaves us more vulnerable, and the world less safe.

Deterrence remains the surest way to prevent a future nuclear crisis, and that requires modernizing and upgrading America’s nuclear arsenal.

President Barack Obama took U.S. nuclear policy in the opposite direction. Deemphasizing the tried and true deterrence model, he took us on a journey the “road to nuclear zero.”

An early milestone was the U.S. commitment to the new START nuclear agreement with the Russians, which placed limits on the types and numbers of nuclear weapons each country could have.

It was one of the most lopsided pacts in history. Only the U.S. had to cut its arsenal. The Russians could build more — which, in fact, they did. The supposed “denuclearization” agreement actually resulted in more nuclear weapons — only all of the new ones were Russian.

Further, the agreement did not cover tactical nuclear weapons where the Russians already had an overwhelming advantage.

The Russians went on to cheat under another pact, the Intermediate Range Nuclear Forces (INF) treaty, by introducing a new class of nuclear weapons.

Again, Obama opted to lead the way to denuclearization by doing nothing. The result: Putin’s arsenal became even larger and more diverse, threatening the delicate balance of deterrent power.

Eventually, even Obama recognized the imprudence of allowing Russian nuclear might to go unchecked and started a modest modernization program of our triad of nuclear delivery systems — air, land and sea.

Under President Donald Trump, America took an off-ramp from the road to zero. The official U.S. Nuclear Posture Review called for a robust upgrade of our nuclear deterrent and negotiating arms control agreements from a position of strength.

The Trump administration withdrew from INF because of Russian cheating and signaled it might not renew the new START when that agreement expires.

This puts the administration on a collision course with the new chairman of the House Armed Services Committee, Rep. Adam Smith (D-Wash.). He wants the administration to “redo” the Nuclear Posture Review, trash its modernization plans and forget about upgrading the triad.

This is not a case of Smith just wanting to “do the opposite” of Trump or feeling nostalgia for the road to zero. He is a long-standing critic of U.S. nuclear policy and the 12-year, $1.2 trillion price tag to modernize it.

The problem is that Smith is stuck in the rose-colored mindset of the post-Cold War era when folks thought nuclear competition was over and done. It’s not.

The great power competition between the U.S. and Russia is back, and nuclear rivalry is part of it. Stability will come from strength not weakness.

That’s the lesson of the last decade. While we walked back the U.S. nuclear deterrent, both Russia and China accelerated.

In showing strength now, Washington won’t be starting a news arms race. It’s already started, with Moscow in the lead. But by getting back in the race, Washington may get the other competitors to back down.

At a bare minimum we should modernize all elements of triad: build the new B-21 bomber; fully deploy the Ohio class submarine and develop the Ground Based Strategic Deterrent, the replacement for the aging Minuteman intercontinental ballistic missile.

The U.S. should also pursue low nuclear yield submarine-launched ballistic and cruise missile capabilities, and continue investing in nuclear infrastructure and the capacity test nuclear weapons, if needed.

Like it or not, we live in an age of nuclear proliferation. “Peace through strength” remains the best path forward, and strength requires both a deterrent nuclear force and effective missile defenses.