One should not take Donald Trump presidential candidacy lightly: White House

Said the Democrats need to mount a serious campaign to ensure that Trump is not elected the next US President

The White House has said that one should not take the candidacy of Republican presidential front-runner Donald Trump lightly, and Democrats need to mount a serious campaign to ensure that the real estate magnate is not elected the next US President.

"We should not take Mr Trump lightly, and that even if he is the Republican nominee, that Democrats are going to need to mount a serious campaign to ensure that he is not elected the next President of the US," White House Press Secretary Josh Earnest said at his daily news conference yesterday.

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"That is certainly why I think you can expect that both the President and the Vice President will be active on the campaign trail, making a forceful case for the Democratic nominee, whether that, frankly, is Secretary (Hillary) Clinton or Senator (Bernie) Sanders," he said.

Meanwhile, the State Department said world leaders have been expressing their concern over the rhetoric coming from presidential candidates.

While State Department Spokesman John Kirby did not name any presidential candidate, officials said the concerns were particularly against Trump, 69.

"I am not going to give you a list, but I can tell you, virtually every foreign leader that the Secretary (of State) meets with expresses concerns about the campaign rhetoric here in the US and expresses a fair bit of angst about where things are going," Kirby said.

"Because these comments do not necessarily, in many cases, reflect certainly the Secretary's view of our foreign policy objectives, or in many cases, our own values as Americans. So virtually all of them have expressed that concern, and he said so," he said.

Trump, meanwhile, said that NATO is obsolete.

"We are spending too much money on NATO. We are paying the lion's share. We are spending tremendous amounts of money on something that was many, many decades ago. And the world has changed," he told Fox News in an interview.

"It is a different place. There is no emphasis on terror with NATO. Frankly, if there is, you need different countries, because it involves different countries. NATO is very obsolete and it should be readjusted and changed," Trump said.

Calling for modernisation of NATO, he said the US should not pay for this.

"We need to modernise NATO, at a minimum modernise it. But certainly we should not be paying for the kind of, we are paying disproportionately so much, and we are a nation that owes $19 trillion. We just can not keep doing this," Trump said, adding that he has the ultimate answer to keeping America safe from radical terrorism.