Former Secretary General Anders Fogh Rasmussen speaks in 2013 | Chip Somodevilla/Getty Images Former NATO chief: Donald Trump is a global risk When America retrenches, it leaves a vacuum that is filled by ‘bad guys,’ says Anders Fogh Rasmussen.

PARIS — Donald Trump's "America First" doctrine would weaken the United States and empower autocrats around the world, said former NATO chief Anders Fogh Rasmussen.

Trump, whom a group of 50 national security advisers have said would be a liability for U.S. security, has piled criticism on his country's NATO partners in Europe, arguing that Americans are paying too much to protect their allies.

In a wide-ranging interview with POLITICO — the full text of which can be read here — Rasmussen condemned the "outrageous" statements by Trump and his supporter Newt Gingrich.

The Republican presidential candidate's ideas were an invitation to "autocrats, terrorists and rogue states" to further test international standards of rule of law, he said.

"His slogan 'America First' is out of touch with what is actually the role of the United States," said 63-year-old Rasmussen, a former Danish prime minister who led NATO until 2014, handling its early response to the conflict in eastern Ukraine.

"The United States has served as the world's leader since the Second World War ... and this international world order has served us very well," said Rasmussen.

"This is of course in America's self interest. For instance, if America were to disengage from Europe, then you would really risk that Russia would increase her influence in Europe, and soon America would experience a more hostile Europe. That wouldn't be in America's interest."

Rasmussen, who now runs a consultancy, insisted that he was not taking sides in the U.S. presidential campaign. He praised both Democratic and Republican administrations and said he had no personal stake in the coming election.

However, Hillary Clinton would be "more determined to defend the United States' allies" than Trump, he said, adding that she had a less ambivalent attitude toward Russia, while Trump has piled praise on Putin, denied the presence of Russian-backed troops in Ukraine, called for the West to accept the annexation of Crimea and urged Russian hackers to retrieve deleted emails from Clinton's accounts.

"He denied the presence of Russian troops in Ukraine, which is ridiculous," said Rasmussen. "It's evident thanks to NATO intelligence that Russian-backed troops are active in eastern Ukraine," said Rasmussen. "All that [ambivalence toward Moscow] is very disturbing to Eastern Europe."

Obama's reluctance

While accusing Trump of ignoring the United States' global role, Rasmussen also observed that Washington had been less assertive under Barack Obama's presidency, with negative effects on stability.

"I do believe that Mr Obama has been too reluctant to use American force to prevent and solve conflicts around the world. It's no coincidence that autocrats, terrorists and rogue states have been more influential at the same time that he has been more reluctant to use military force," he said.

"When America retrenches and retreats, it leaves behind a vacuum, and that vacuum is filled by bad guys."

Rasmussen reiterated his criticism of European countries for spending too little on defense at a time when Russia is growing more assertive; In 2015, just five NATO allies met its statutory requirement to spend 2 percent of gross domestic product on defense.

But he sees the trend changing: "I think 2015 will represent the lowest level of defense spending in the postwar period. From here we will see more defense spending in Europe ... In Eastern Europe you will see a faster increase, which is partly explained by the Russian aggression in Ukraine. Personally, I think it is very slow, but it's a development in the right direction."

However, even a sizeable increase in European defense spending would not replace the United States' heft as global superpower.

"My appeal to the next president is that we need a global policeman, and that policeman should be the United States," Rasmussen said. "We don't have any other."