'We're a poor country now': Donald Trump wants America to spend at home

But subjected to forensic questioning on Monday, Trump revealed that what he really wants is to stay at home and build stuff.

Nation-building is so yesterday; isolationism is smarter than intervening; and it's time the rest of the world paid its own way.

On a day when Trump and Hillary Clinton snipped at each other at a mass gathering of Israel supporters, Trump was subjected to the most detailed questioning to date on foreign policy in a recorded meeting with the editorial board of The Washington Post.

His thesis was that much of the existing US global security infrastructure is too costly and returns little for Washington's investment - it was time for the likes of the NATO countries, Japan, South Korea and Saudi Arabia to fund their own security.

Abandoning decades of Republican orthodoxy on the essential need to project American power across the world, Trump said: "I don't think we should be doing nation-building any more.

"We spent billions of dollars on Saudi Arabia and they have nothing but money, and I say 'why?'. I would structure a much different deal with them, and it would be a much better deal."

Asked if there was nothing for the US in its global security posture, Trump replied: "We're not in the position we used to be - I think that we were a very powerful, very wealthy country; we're a poor country now - a debtor nation.

"NATO is costing us a fortune and yes, we're protecting Europe with NATO, but we're spending a lot of money.

"Ukraine is a country that affects us far less than it affects other countries in NATO and yet we're doing all the lifting, they're not doing anything. And I say, why is it that Germany is not dealing with NATO on Ukraine? Why is it that other countries that are in the vicinity of Ukraine are not dealing with it?"

Trump twice offered that he'd be unwilling to trigger a third world war, whether over the Russia-Ukraine conflict or China's ambitions in the South China Sea. Similarly, he reneged on earlier comments that were read as a willingness to dispatch 20,000 to 30,000 troops to the Middle East to challenge the so-called Islamic State.

"I would put tremendous pressure on other countries that are over there to use their troops, and I would give them tremendous air support … because we have to get rid of [Islamic State]," he said.

Trump complained that the US had built and rebuilt schools in Iraq as many as three times as they were bombed over and over, "and yet we can't build a school in Brooklyn".

"At what point do you say, 'hey, we have to take care of ourselves?' So I know the outer world exists and I'll be very cognisant of that. But at the same time our country is disintegrating, large sections of it, especially the inner cities."

So how would a President Donald Trump have handled recent crises and conflicts?

The Iran nuclear deal: He would not have given Tehran access to more than $US100 billion ($131 million) of its own money that had been frozen by sanctions and he would not have commenced negotiations without the release of all American prisoners held by Iran. "They would have said 'no', and we would have said 'double up the sanctions', and within a short period of time we'd have had our prisoners back."

The South China Sea: "We have rebuilt China - they have drained so much money out of our country that they have rebuilt China," he said. "Without us, you wouldn't see the airports and the roads and the bridges … We don't build any more - we've had our day." Claiming a trade war would force a Chinese retreat, he argued: "You start by making it tougher. They're selling their products to us for … you know, with no tax, no nothing."

The US-led invasion of Iraq: Describing it as one of the worst decisions made in US history, Trump nonetheless identified a missed opportunity. "I would have defended the areas with the oil and I would have taken out a lot of oil. And, uh, I would have kept it … because, look – Iran has the oil and they're going to have [the Iraqi oil] they don't have because Iran is taking over Iraq as sure as you are sitting there."

Speaking to thousands at the Washington conference of the American Israel Public Affairs Committee, Hillary Clinton sought to skewer Trump - without naming him - for his offer to be "neutral" in any effort to broker peace between Israel and Palestine: "We need steady hands, not a president who says he's neutral on Monday, pro-Israel on Tuesday and who-knows-what on Wednesday."

Trump's own speech included some of the time-honoured mantras of US support for Israel, "our strategic ally … our cultural brother, the only democracy in the Middle East", and condemned the Obama administration and Hillary Clinton's role in the conflict as "a total disaster".

But Trump being Trump, there was a domestic angle too.

"I love the people in this room, I love Israel," he told the conference. "My daughter Ivanka is about to have a beautiful Jewish baby."