Washington: Democratic presidential frontrunner Hillary Clinton suggested a Donald Trump presidency would be 'Christmas for the Kremlin' only to have her billionaire rival hit back branding her incompetent.
"If Mr Trump gets his way, it'll be like Christmas in Kremlin," she said in an address Wednesday at Stanford University, California targeting Trump for his recent comments that the US should limit its involvement with Nato.
Warning such a move would only be a boon for Russian President Vladimir Putin, "who already hopes to divide Europe," Clinton said, "It will make America less safe and the world more dangerous.
"When it comes to the struggle against Islamic State, we need our allies as much as ever. We need them to be strong and engaged for they are increasingly on the front lines," she said describing Nato as "one of the best investments America has ever made."
In her speech on terrorism in the wake of the attacks in Brussels, the former secretary of state also attacked Trump's closest rival Ted Cruz, who on Tuesday called for patrolling Muslim neighbourhoods in the US as a way of combating Islamic State.
"When Republican candidates like Ted Cruz call for treating American Muslims like criminals, and for racially profiling predominantly Muslim neighbourhoods, it's wrong, it's counterproductive, it's dangerous," Clinton said.
"One thing we know that does not work is offensive inflammatory rhetoric that demonizes all Muslims," she added. "These Americans are a crucial line of defense against terrorism."
Clinton also blasted the Republican candidates for condoning torture as a means of fighting terrorists.
Donald Trump was quick to respond to Clinton's attacks.
"Just watched Hillary deliver a prepackage speech on terror. She's been in office fighting terror for 20 years -- and look where we are!" he tweeted.
Donald Trump also branded Clinton as incompetent questioning his rival's capability to be commander-in-chief.
"I think people will see I'm much more competent than she is," Trump told Bloomberg Politics' "With all due respect, I think I'm much smarter than she is. I think I'm much more competent than she is."
Trump's used the same phrase during an appearance on Fox News' Tuesday. "Incompetent Hillary doesn't know what she's talking about," he said. "She doesn't have a clue. She's made such bad decisions."
Trump later took to Twitter to re-up his new phrase.
"Incompetent Hillary, despite the horrible attack in Brussels today, wants borders to be weak and open-and let the Muslims flow in," he tweeted. "No way!"