"I'm not going to cut Social Security like every other Republican and I'm not going to cut Medicare or Medicaid," Donald Trump declared in 2015. "Every other Republican's going to cut, and even if they wouldn't, they don't know what to do because they don't know where the money is. I do. I do."

As regular readers may recall, this became a staple of his entire national candidacy: no matter what, Americans could count on him to champion these social-insurance programs. Ahead of the 2016 race, Trump wanted everyone to know that entitlement cuts, as far as he's concerned, are off the table.

The Republican has apparently changed his mind, as we were reminded last night during a presidential town-hall forum in Scranton, Pennsylvania.

When Fox News host Martha MacCallum suggested that if "you don't cut something in entitlements, you will never really deal with the debt," Trump jumped in right away. "Oh, we'll be cutting," he said to an audience in Scranton. "We're also going to have growth like you've never seen before."

For now, let's put aside Trump's promise to generate unprecedented economic growth. He made similar promises four years ago, but he's failed spectacularly to meet his own goals.

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Instead, it was the "we'll be cutting" part of his answer that's likely to cause the president some trouble.

Trump also addressed this in late January, when CNBC's Joe Kernen sat down with the president and asked whether entitlement cuts would ever be on the Republican's plate. "At some point they will be," Trump replied, adding, "[A]t the right time, we will take a look at that."

When Kernen followed up, asking about Trump's willingness to "do some of the things that you said you wouldn't do in the past," the president added, "We're going to look."

As of last night, however, Trump doesn't just intend to look; he also intends to cut.

What's more, as we've discussed, there's a larger context to this that includes Larry Kudlow, the director of the Trump White House's National Economic Council, arguing in the not-too-distant past that the president's team is prepared to look at entitlement "reforms" -- which is a common euphemism for cuts.

As CNBC reported a year and a half ago, Kudlow added that the Trump White House was determined to reduce federal spending, and "part of the Republican plan to curb spending is tackling entitlements."

No matter who wins the Democratic presidential nomination, Trump and his team have made this a key 2020 issue, on which Republicans will be on the unpopular side.

Josh Schwerin, the communications director for Priorities USA, a leading super PAC affiliated with Democratic politics, noted overnight that focusing on the president's entitlement cuts "is consistently the top testing hit on Trump." Last night, the Republican made this line of attack even more potent.

Update: According to the White House, the president's comments were intended to refer to cutting deficits, not cutting entitlements. In context, I'm not entirely sure whether that explanation makes sense, but that's apparently the new Team Trump line.