Donald Trump and Hillary Clinton battled sharply over the influence of Russian President Vladimir Putin during the last presidential debate in Las Vegas.
Mrs Clinton called Mr Trump the Russian president's puppet and Mr Trump fired back that Mr Putin had repeatedly outsmarted Mrs Clinton.
Mrs Clinton said Mr Trump had refused to condemn Mr Putin and Russia for recent cyber attacks.
US intelligence agencies and the Department of Homeland Security have said the Russian leadership was responsible for recent cyber attacks on the Democratic National Committee and the leaking of stolen emails.
"He'd rather believe Vladimir Putin than the military and civilian intelligence officials that are sworn to protect us," Mrs Clinton said.
However, Mr Trump rejected the idea that he was close with Mr Putin, but suggested he would have a better relationship with Russia's leader than Mrs Clinton.
"He said nice things about me," Mr Trump said. "He has no respect for her, he has no respect for our president and I'll tell you what, we're in very serious trouble."
Mrs Clinton responded: "Well that's because he'd rather have a puppet as president of the United States."
"No, you're the puppet," Mr Trump retorted.
Asked if he condemns any interference by Russia in the US election, as suggested by Mrs Clinton, Mr Trump states: "By Russia or anybody else? Of course I condemn. I don't know Putin ... Let me tell you Putin has outsmarted her and Obama every single step of the way."
"Putin has outsmarted her and Obama every single step of the way," he said in a reference to US President Barack Obama, a Democrat like Mrs Clinton.
Mrs Clinton also said Mr Trump had been "cavalier" about nuclear weapons and should not be trusted with the nuclear codes.
On Mr Trump's plans to build a wall on the US-Mexican border, he said, "We need strong borders".
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"In the audience tonight we have four mothers of, I mean these are unbelievable people that I’ve gotten to know over a period of years, whose children have been killed, brutally killed, by people that came into the country illegally," said Mr Trump.
"They are coming in illegally. Drugs are pouring in through the border. We have no country if we have no border. Hillary wants to give amnesty she wants to have open borders," added Mr Trump.
Mr Trump stated that one of the first things he will do if he is elected is to strengthen immigration, build a wall and round up the drug lords, adding "we have some bad hombres here and we are going to get 'em out".
