GEOFF BENNETT: Responding to a reporters question, Ukrainian President Zelenskyy dismissed the idea that Ukraine might lose the war to Russia.

But his country is waiting on more support from the U.S. and the European Union, and that aid is crucial for Ukraine's air defense, which is becoming more important as Russia begins what appears to be another winter-long campaign of strikes on Ukraine's infrastructure.

Nick Schifrin and Eric O'Connor report from Central Ukraine.

NICK SCHIFRIN: It was the winter of Ukraine's disconnect.

A Russian campaign targeted Ukraine's critical infrastructure and left this power plant burned out and gutted.

Russia hoped to engineer a humanitarian crisis and sap Ukraine's will to fight.

It failed.

But attacks on this plant alone left more than 18,000 people without power or heat, and they almost killed shift manager Oleksandr.

OLEKSANDR, Power Plant Shift Manager (through translator): We heard the sound of a missile.

I only managed to shout to my partner "Get down" before we heard the first explosion.

The windows blew out and parts of the ceiling fell.

Then, we started hearing more explosions.

NICK SCHIFRIN: His dedication to the plant goes back decades.

His father was an engineer here in the '80s and '90s.

Last winter, Russian missiles and suicide drones hit the plant three times.

They caused catastrophic damage, including to the units that create power and distribute it.

Attacks like this caused $10 billion of damage and affected 12 million Ukrainians.

And U.S. and Ukrainian officials believe winter is coming again.

OLEKSANDR (through translator): We are preparing physically.

We are preparing equipment.

We are preparing mentally.

It's scary.

Of course, it's scary.

But electricity is the lifeblood of the economy.

We have to maintain it.

NICK SCHIFRIN: In the last few weeks, Russia has launched drones and ballistic missiles that targeted Ukrainian critical infrastructure.

The threat is now constant.

Almost every night, the air raid sirens sound, the spotlights hunt, and Ukraine's air defense engages.

Heavy machine guns target an Iranian-designed Shahed drone.

On this front, Ukraine claims widespread success.

Last week, it said it shot down 104 out of 112 Shahed drones.

Outside of Kyiv, Mykyta shows the remnants of shot-down Shahed drones.

Each can carry 100 pounds of explosives.

He says his air defense unit is getting better, but so are Russian drones.

MYKYTA, Ukrainian Commander (through translator): Before, when Shaheds were first used, they were less maneuverable, easier to see and louder.

Their thermal footprint was also larger.

Now the heat footprint is much smaller, they have become quieter, and it has become harder to see them on radar.

NICK SCHIFRIN: Ukraine has long relied on Soviet-produced air defense.

But the missiles aren't made in the West, and, earlier this year, Ukraine started running out.

So Ukraine's air defense is now a melting pot of Western munitions that the Ukrainian air force shows off in online videos.

They include the German IRIS-T, American Patriots that have hit some of Russia's most advanced missiles, and the U.S. Norwegian Advanced Surface to Air Missile System, or NASAM.

It protects Washington, D.C., and is the system that Mykyta fires.

Why do you have to use the expensive NASAM system against a relatively cheap drone?

MYKYTA (through translator): We have no choice.

Despite the fact that these drones are very cheap, they cause a lot of pain.

And they are also a means to exhaust our air defense.

NICK SCHIFRIN: Do you have enough?

Do you have enough weapons systems and missiles in order to do your job?

MYKYTA (through translator): We don't have enough weapons or ammunition.

Our enemy is launching attacks on our country nonstop.

Our enemy doesn't hit twice in the same spot.

The enemy is changing its tactics.

And the only way to counter that is to increase our anti-missile capabilities.

JOE BIDEN, President of the United States: We will continue to supply Ukraine with critical weapons and equipment as long as we can.

NICK SCHIFRIN: But U.S. and Ukrainian officials are worried that funding impasses in Congress and in the European Union could mean Ukraine runs out of air defense munitions.

VOLODYMYR ZELENSKYY, Ukrainian President: Who controls the skies controls the war's duration.

NICK SCHIFRIN: Ukrainian officials say they will have to increasingly rely on their own ingenuity and mobility.

This mobile unit says it survives Russian attempts to destroy Ukrainian air defense because it's never in the same place twice.

The mobile units complement the large Western air defense to create what's known as defense in depth.

Around Kyiv, the various systems are coordinated by Colonel Serhii Yaremenko, who says, this winter, they are applying lessons learned from last winter.

COL. SERHII YAREMENKO, Ukrainian Brigade Commander (through translator): We are stronger.

We have more experience.

We know the main flight routes of their cruise missiles.

We are taking preventive measures in order to effectively counteract the intentions and mission of the enemy.

NICK SCHIFRIN: Back at the power plant, workers are trying to repair the plant as quickly as possible.

It may not look like it, but they have repaired enough to once again power the local community.

For Oleksandr, that success isn't only about continuing his father's legacy.

It's also about lighting his family's future.

That's his daughter, 24-year-old Daria, the plant's press officer.

DARIA, Power Plant Shift Manager: They work in really rough conditions, but they do, and they do their best.

NICK SCHIFRIN: They still have a lot of repairs.

And they know the winter will be long.

But they feel resilient, and they're determined that this plant will provide rays of hope, no matter what this winter brings.

DARIA: We have a project which is called (SPEAKING IN FOREIGN LANGUAGE).

It's kind of like the brave ones who bring the light, because that's what they actually do.

That's our future.

We want to be free.

Our people, when they are united, they are a strong force.

NICK SCHIFRIN: Her father echoes her determination.

She translates.

DARIA: No matter what, we are going to stay strong, and yes, just do what we do, yes.

NICK SCHIFRIN: And so, after a break, it's back to work.

As the sign says, "If we got through this winter, we can get through anything."

For the "PBS NewsHour," I'm Nick Schifrin in Central Ukraine.