Republican presidential candidate Donald Trump has said he will end the Russia-Ukraine war if he wins the November presidential elections, an assertion dismissed by his Democratic rival Kamala Harris who said the former US president would "just give up".

Trading barbs with Vice President Harris on Tuesday at their first presidential debate in Pennsylvania ahead of the US general elections on November 5, Trump said the war would have never started had he been the president.

“I'll get the war with Ukraine and Russia ended. If I'm president-elect, I'll get it done before even becoming president,” Trump, 78, said in response to a question during the debate.

Asserting there was no threat of war in the four years he was president from 2017 to 2021, Trump said, "I know (Russian President Vladimir) Putin very well. He would have never -- and there was no threat of it either, by the way, for four years -- gone into Ukraine and killed millions of people when you add it up...” Trump blamed the Biden-Harris Administration for not preventing the war in Ukraine and said, "If I were president, it would have never started." The former president asserted that he wanted the war to stop and claimed that millions were being killed in it.

“I want to save lives that are being uselessly people being killed by the millions. It's the millions. It's so much worse than the numbers you're getting, which are fake numbers," he said.

“I know (Ukrainian President Volodymyr) Zelenskyy very well and I know Putin very well. I have a good relationship. They respect me, they don't respect (incumbent President Joe) Biden,” he said.

“How would you respect him (Biden)? He hasn't even made a phone call in two years to Putin. He hasn't spoken to anybody. That is a war that's dying to be settled. I will get it settled before I even become president if I win when I'm president-elect,” Trump said.

Disagreeing with him, Vice President Harris said, "I believe the reason that Donald Trump says that this war would be over within 24 hours is because he would just give it up. And that's not who we are as Americans.” Harris said she met Zelenskyy and shared "American intelligence about how he could defend himself" a few days before the Russian invasion and went to NATO's eastern flank to Poland and Romania days later, bringing 50 countries together to support Ukraine in its "righteous defence".

"Because of our support, because of the air defence, the ammunition, the artillery, the javelins, the Abrams tanks that we have provided, Ukraine stands as an independent and free country," she said.

"If Donald Trump were president, Putin would be sitting in Kyiv right now and understand what that would mean because Putin's agenda is not just about Ukraine,” she said.

Addressing Trump, she said, "Understand why the European allies and our NATO allies are so thankful that you are no longer president and that we understand the importance of...NATO. And what we have done to preserve the ability of Zelenskyy and the Ukrainians to fight for their independence. Otherwise, Putin would be sitting in Kyiv with his eyes on the rest of Europe, starting with Poland.” During the debate, Trump claimed that when Putin endorsed Harris last week saying 'I hope she' wins, the Russian President meant it "because what he's gotten away with is absolutely incredible".

"It wouldn't have happened with me. The leaders of other countries think that they're weak and incompetent and they are grossly incompetent,” he said, referring to the Biden-Harris administration.

Harris alleged it was well known that Trump was weak and wrong on issues of national security and foreign policy.

“It is well known that he admires dictators (and) wants to be a dictator on day one, according to himself. It is well known that he said of Putin that he can do whatever the hell he wants and go into Ukraine. It is well known that he said when Russia went into...,” she said.

“In Ukraine, it was brilliant, it is well known. He exchanged love letters with (North Korean leader) Kim Jong Un. It is absolutely well known that these dictators and autocrats are rooting for you to be president again because they're so clear they can manipulate you with flattery and favours," she said.

Alleging that military leaders with whom Trump has worked have told her that he is a "disgrace", Harris said, "That is why we understand that we have to have a President who is not consistently weak and wrong on national security, including the importance of upholding and respecting in highest regard our military.” This was the second presidential debate, but the first between Trump and Harris. The first presidential debate in Atlanta on June 27 was between Trump and President Biden. Following his terrible performance at the debate, Biden withdrew from the race and paved the way for Harris to be the Democratic Party’s nominee for the November elections.

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