Central to President Trump’s appeal for much of his base is the hard line he takes on immigration. From the first minutes of his campaign launch announcement in June 2015, Trump excoriated illegal immigration and embraced the idea that one of the key priorities for the next president should be to crack down on those in the country illegally.

Over and over during the 2016 campaign, while his immigration rhetoric solidified a lead in the Republican primaries and into the general election, Trump reminded voters that he planned to focus on illegal immigration as president. In particular, he would point to a system called E-Verify. E-Verify allows employers to check information provided by employees with government records to establish whether the employees are allowed to work in the United States.

The checks are conducted online, as shown below.

During a town-hall event in March 2016, MSNBC’s Chris Matthews asked Trump about his plan to address the hiring of undocumented workers.

“Well, you can do that with E-Verify and the various methods,” Trump told Matthews. He told Matthews that the Trump Organization used the system, which, The Post would later report, wasn’t universally true. The punishment for hiring an undocumented worker? Trump proposed that it should be “a huge financial penalty” — or perhaps a criminal penalty.

Again, it was of a piece with his broader rhetoric: Immigrants should be dissuaded from entering the country illegally, and there should be efforts to curtail their ability to work in the United States to tamp down on illegal immigration. Among the changes the administration implemented to the immigration system last month was a tightening of rules on obtaining work permits.

It was a bit incongruous, then, that Trump said in an interview on “Fox News Sunday” that there might be some exceptions made. Trump was asked by the network’s Steve Hilton whether E-Verify would be part of the proposed immigration overhaul Trump unveiled in vague terms last week.

“E-Verify is going to be possibly a part of it,” Trump replied. “The one problem is E-Verify is so tough that in some cases, like farmers, they’re not — they’re not equipped for E-Verify. I mean, I’d say that’s against Republicans. A lot of the Republicans say you go through an E-Verify."

Trump said he used it during construction at the Trump Organization hotel on Pennsylvania Avenue — a project that The Post found probably included undocumented workers. They’d go through some 30 applicants before they found one who was eligible to work in the country, Trump said.

“So it’s a very tough thing to ask a farmer to go through that,” Trump said. “So in a certain way, I speak against myself, but you also have to have a world of some practicality.”

It’s an interesting shift in Trump’s rhetoric. It’s probably not unexpected; there have been numerous stories about farmers who have expressed concern about their ability to bring in their crops without the use of undocumented labor.

A 2015 report from Pew Research Center found that only 5 percent of immigrants in the country illegally worked in agriculture, more than twice the rate of employment among U.S.-born workers. But some 16 percent of workers in the industry were undocumented, Pew estimated.

The next most densely populated industries? Construction at 12 percent and leisure and hospitality at 9 percent. Both industries are ones in which the Trump Organization is active, from constructing or refurbishing facilities such as the Trump International Hotel in Washington to staffing his resorts and golf courses. Last year, The Post reported that the Trump Organization had begun cracking down on undocumented employees at its facilities.

So why now? Why is Trump willing to give farmers a pass on this issue that was so central to his campaign?

One likely reason is that Trump’s trade war with China has had broad negative ramifications for U.S. agriculture. After the administration imposed a number of new tariffs on products from China, China retaliated by adding a tax on imports of U.S. goods, including products such as soybeans. In an effort to lighten the effect of the trade war, the government has paid affected farmers more than $8.5 billion to offset their losses.

It’s a moment, in other words, when Trump’s actions have hurt farmers, an effect that ripples through the largely rural communities where agriculture is dominant — and which heavily voted for Trump in 2016. With his reelection looming, there’s a political incentive for Trump to refrain from adding other burdens to these communities.

During the campaign, Trump specifically suggested that farmers who needed workers to, say, pick grapes (as at the Trump winery in Virginia) could bring people in on work visas — an obviously more complicated process than verifying employment through E-Verify. (Trump Organization properties have often used work visas to hire as well.)

Now, though, his tune has changed. During 2016, his hard line on immigration resonated with his base of voters. As president — as a president seeking reelection — he’s acknowledging that perhaps there’s more nuance involved than he used to suggest.