For seven decades, America’s strength, security and prosperity have been underpinned by our unmatched network of treaty alliances, cemented in shared democratic values and a recognition of our common security. But after three years of Donald Trump’s insults and antics, our alliances are under enormous strain.

The damage done by the president’s hostility toward our closest partners was on full display at this week’s gathering of Nato leaders in London, which should have been an unequivocal celebration of the 70th anniversary of the most successful alliance in history.

The success of Nato was not inevitable, easy or obvious. It is a remarkable and hard-won accomplishment, and one based on a recognition that the United States does not become stronger by weakening our allies. But that is just what Trump has done, repeatedly and deliberately.

He treats our partners as burdens while embracing autocrats from Moscow to Pyongyang. He has cast doubt on the US commitment to Nato at a moment when a resurgent Russia threatens our institutions and freedoms. He has blindsided our partners on the ground in Syria by ordering a precipitate and uncoordinated withdrawal. He has attempted to shake down South Korea and Japan, evidently mistaking our security alliances for protection rackets. And he has wrecked US credibility by unilaterally tearing up our international agreements on arms control, non-proliferation and climate change.

This reckless disregard for the benefits of our alliances comes at a perilous moment

This reckless disregard for the benefits of our alliances comes at a perilous moment, when we face common threats from powerful adversaries probing the weaknesses of our institutions and resolve. Longstanding allies in Asia are doubting our reliability and hedging their bets. Russia’s land grab in Ukraine has upended the post-1989 vision of a Europe “whole, free, and at peace”. The chaotic Brexit process has consumed our closest partners, while sluggish growth and rising xenophobia fuel extremist politics and threaten to fracture the European Union.

A mounting list of global challenges demand US leadership and collective action. As president, I will recommit to our alliances – diplomatically, militarily and economically. I will take immediate action to rebuild our partnerships and renew American strategic and moral leadership, including by rejoining the Paris climate accord, the United Nations compact on migration, and reaffirming our rock-solid commitment to Nato’s article 5 provisions.

But we must do more than repair what Trump has broken. Instead we need to update our alliances and our international efforts to tackle the great challenges of our age, from climate change and resurgent authoritarianism to dark money flows, a weakening international arms control regime and the worst human displacement crisis in modern history.

This means revitalizing our state department and charging our diplomats to develop creative solutions for ever more urgent challenges. It means working with like-minded partners to promote our shared interest in sustained, inclusive global economic growth and an international trade system that protects workers and the environment, not just corporate profits. And it means reducing wasteful defense spending and refocusing on the areas most critical to our security in years to come.

Alliances are not charities, and it’s fair to ask our partners to do their share. I will build on what former president Barack Obama started by insisting on increased contributions to Nato operations and common investments in collective military capabilities.

But I will also recognize the varied and significant ways that European states contribute to global security – deploying troops to shared missions, receiving refugees and providing development assistance at some of the highest per capita rates in the world.

The next president must tackle our common problems using the lessons of common defense. Together, we can counter terrorism and proliferation. We can make common cause in constructing new norms and rules to govern cyberspace. We can dismantle the corruption, monopolies and inequality that limit opportunity around the world and take on the increasingly grave threats to our environment.

We can and will protect ourselves and each other – our countries, our citizens and our democracies.