Ukraine’s president, Volodymyr Zelensky, has said it many times: If Western military support were to falter, the Ukrainians would continue to fight.

They would do it alone if need be, their backs to the wall, at a terrifying human cost.

They would be in largely the same situation they were in during the first phase of Russia’s full-scale invasion. After all, the Ukrainians had to wait months to more than a year for the United States to provide the weapons they needed. During those long months, the courage of the Ukrainians and the talent of their commanders were enough to hold off a Russian military whose troops still were fresh, motivated and sure of themselves.

In a worst-case scenario in which Congress continues to refuse to approve the funds requested by President Biden and Europe follows suit in withdrawing support, the conflict would revert to those early stages. And the Ukrainian forces, which I’ve observed for two years while making three documentaries from the front lines, would shift to a long and grueling war of resistance.

But they would not lay down their arms. This war is existential. Of this I am sure.

So here’s the question: Given that the war will go on, are we going to prolong the fighting or shorten it?

Are we going to allow civilian deaths to pile up or try to minimize them?

Will the United States, for vile political reasons, let the conflict fester and encourage authoritarian and anti-American forces throughout Europe? Or will it decide to come to the aid of its natural and reliable allies in Ukraine?

What message will the country choose to send to imperial China, neo-Ottoman Turkey and an Iran racing toward the nuclear threshold? Will America welcome a multipolar world in which unchecked dictatorships once again lay down the law? Or, having abandoned its allies in Kabul, Aleppo, Erbil and Yerevan, will the country pull itself together behind Kyiv because it’s never too late to correct a series of mistakes?

If it’s the latter — if enough Republicans reconnect with the spirit of Reagan and enough Democrats remain faithful to that of Kennedy; if they want the world’s people to know they are right to rebel and to dream of liberal democracy — then American and allied aid must urgently flow to Ukraine.

European Storm Shadow cruise missiles must be delivered to the Zaporizhzhia region to enable the men and women of the 47th Separate Mechanized Brigade — which took the village of Robotyne last summer in bold commando operations — to push south past Russian fortifications toward occupied Verbove, Tokmak, Berdyansk and the Azov Sea.

Ukrainian drone pilots — who have demonstrated since the early days of the war that no Russian ammunition depot, naval base or ship in Crimea is out of their reach — must receive the long-range U.S. Army Tactical Missile Systems, known as ATACMS, promised since September, which they need to fully open the Black Sea.

F-16s, whose arrival near Donbas is equally overdue, are an essential complement to the artillery and infantry units working to liberate the Bakhmut and Avdiivka zones and the routes in and out of Donetsk and Luhansk.

To the south, in the Kherson zone, which was liberated more than a year ago by unassisted Ukrainian forces, the need is for river-crossing gear, amphibious equipment and light Bradley tanks. That would enable the Ukrainian commandos under the command of Maj. Gen. Andriy Kovalchuk to expand the operations I watched them conducting on far too small a scale to the eastern side of the Dnipro River, near the villages of Krynky, Kozachi Laheri and Korsunka.

Additionally, Ukraine needs an “iron dome” worthy of the name to replace the mobile antiaircraft units I accompanied in makeshift pickup trucks as they chased drones headed for major Ukrainian cities, trying to shoot them down with bazookas. I have been saying since Day 1 that helping the Ukrainians close the sky is essential.

For the most part, these weapons are readily available in American and European stockpiles. They come at a cost, of course. But that cost is far lower than that of a defeated Ukraine, which could well embolden Russia to go after a NATO country and force a full-scale U.S. and European intervention.

Our defense budgets today are half what they were during the Cold War — and of what they will have to be if we allow Russia to become an offensive threat again. While we hesitate to pay our respects to international law in dollars, the Ukrainians are paying in blood.