Washington (CNN) One of Donald Trump's many memorable lines on the campaign trail was about ISIS.

"I would bomb the s**t out of 'em. I would just bomb those suckers," he said.

Given that, launching the so-called "mother of all bombs" against an ISIS target makes a lot of sense.

Under normal circumstances, that consistency -- a campaign vow with high-profile follow through -- is standard. It is expected. But not with this President, and certainly not this week, where a slew of his decisions and pronouncements were completely at odds with what he told voters. For instance:

Trump, in May, 2016: "NATO is obsolete."

Trump, this week: "I said it was obsolete; it's no longer obsolete."

Again, Trump last May: "China has been ripping us off. The greatest abuser of the history of this country,"

And, Trump this week on China's leader: "President Xi wants to do the right thing. We had a very good bonding."

Changing positions is hardly new for Donald Trump. After all, not long before he ran as an anti-abortion, anti-Obamacare Republican, he was a supporter of abortion rights and a universal health care system.

When I interviewed Trump early in his campaign about it, he was unapologetic.

JUST WATCHED Trump shifts: Flexibility, evolution or flip-flop? Replay More Videos ... MUST WATCH Trump shifts: Flexibility, evolution or flip-flop? 08:01

"People are losing their plans. They're losing their doctors. Doctors -- one of the biggest problems that nobody talks about, doctors are all leaving. They're leaving the profession," Trump told me in July 2015.

That kind of flip-flop would crush most candidates' campaigns. Not Trump. Voters were drawn to him for lots of reasons, but being dogmatic was NOT one of them.

In fact, the President himself was introspective about it last week, as he previewed military strikes in Syria -- which he had not long ago railed against.

"I like to think of myself as a very flexible person. I don't have to have one specific way, and if the world changes, I go the same way," Trump said.

To be sure -- on many of his 180s, from NATO to Syria -- the world has NOT changed. So, the question is, what has? Sources close to Trump tell me there are several ways to answer that question.

First, the obvious. He is a novice to politics and foreign policy who is getting a high-stakes, on-the-job education, which is leading him to change some views.

Second, he is and always will be a businessman driven by results, not ideology. For example, he didn't think NATO was serving America's interest. Now that he is involved, he clearly believes he can change that.

Third, and maybe most importantly, now that he is settling in as president, his inner circle has expanded, and along with it, his world view. New confidantes like Defense Secretary Gen. James Mattis and National Security Adviser HR McMaster, who both support being tougher on Syria and more open to NATO, have the President's ear. Advisers like Steve Bannon and Stephen Miller, supporters of the "America First" language of the Trump campaign and inauguration, now have company and competition from those with more globalist points of view.

"Finally this week we saw realism from the Trump administration. It's very welcome," said former US ambassador to NATO and veteran diplomat Nicholas Burns.

Some sources say the President is most influenced by the last person who talked to him. Others say that's not quite right. A senior administration official with the President every day says that it is true he is swayed by aides, advisers, friends, members of Congress and others he talks to who try to influence him. But this source insists that it is not necessarily the last argument that the President hears that wins out, it's the one he thinks is most cogent and compelling.

An easy way to look the President's outward turn toward the world in the last week is that it is proof that Bannon, whom the President publicly took to the woodshed over infighting with Trump son-in-law Jared Kushner, is on the outs -- and along with that, so are his nationalistic policies.

A simple way to see it is that as a result, the more hawkish advisers are ascendant and more influential.

The same senior administration official laughs that off, insisting that is "giving us all too much power."

"I have seen him brush back everyone, and by everyone, I mean everyone," said the official, "even those most people think could never get fired."