THE MORNING PLUM:

President Trump is intensifying his confrontation with special counsel Robert S. Mueller III — to the point that he may defy a subpoena for an interview — even as Trump and Republicans appear to be increasingly relying on the idea that the Mueller probe is a “witch hunt” to galvanize the base in the midterm elections.

That’s potentially a recipe for much worse to come.

Over the weekend, Trump lawyer (sic) Rudy Giuliani went on ABC’s “This Week” and openly stated that “we don’t have to” comply if Mueller issues a subpoena to try to compel the president to testify in a sit-down interview. While it’s possible that Mueller and Trump’s lawyers will compromise on a limited sit-down, Mueller is privately threatening a subpoena, and any resulting impasse would go all the way to the Supreme Court.

That’s a confrontation Trump would likely lose. But whether or not Trump is aware of that possibility, it’s now clear that the confrontation itself is what Trump wants — as a way to galvanize his voters heading into the midterm elections.

Politico reports this morning that Trump’s team actively wants to frame the midterms as a referendum on whether his presidency should survive, by arguing that a Democratic-led Congress would result in impeachment. This strategy is favored by the former keeper of the Trumpist flame, Stephen K. Bannon, who is explicitly arguing that the GOP tax cuts won’t be nearly as successful in turning out the base:

“You’ve got to make it an up or down vote Nov. 6. I want Trump on the ticket in every district,” Bannon said in an interview. “You have to put Donald Trump on the ticket. You’re not voting for Congress. You’re voting for Donald Trump.”

One imagines that Democrats will seize on this quote: Yep, Trump is on the ticket in every district. And by the way, it isn’t just Bannon. Other GOP strategists have explicitly said that a war with Mueller will turn out the base. As one of them recently put it: “Voters see themselves in this fight with the president.”

It is certainly true that Republican voters view things this way. But independent voters do not. A recent Post-ABC News poll found that 70 percent of independents support Mueller’s probe into possible Russia-Trump campaign collusion, and 65 percent of them support his probe of Trump’s business activities. And a recent Quinnipiac poll found that 58 percent of independents say Mueller’s probe is fair.

As Amy Walter recently pointed out, even if Republican voters do “come home” to the GOP candidates this fall, a big question will be which way undecided and independent voters break — and right now, they don’t like the president. Given this and the broad support among independents for the Mueller investigation, it’s hard to see how a sustained confrontation with him will help GOP candidates among those voters.

But those GOP candidates will be required to rally behind the president and against Mueller, or risk depressing the base. Indeed, as Walter also notes, Republicans worry that GOP voters, as it is, are not as energized as Democrats, who are super-charged for the midterms. In swing districts, even successfully driving up GOP turnout might not be enough if independents break against the GOP, but betting it all on energizing the GOP base may be all they have left.

So Republicans appear to be lashed to Trump as he goes all-in against Mueller. This morning, Trump tweeted that the Mueller probe is a “Phony Witch Hunt,” and for good measure said this:

Trump is openly admitting that efforts now being investigated as obstruction of justice did, in fact, constitute “fighting back” against a legitimate investigation into conduct by him and his top campaign officials. But this is the whole point: The message is that Trump is fighting the investigation, and his voters are not only persuaded that it’s a witch hunt; they also “see themselves in this fight with the president,” as the GOP strategist quoted above put it.

But this could further alienate independents and swing voters. And so the strategy of increasingly relying on the Mueller “witch hunt” to galvanize GOP voters looks like a fallback effort to hang on to districts that are heavy enough on Republican voters to remain in the GOP column even if independents break bigly for Democrats, provided that GOP turnout is sufficiently energized. And as we’re seeing in multiple GOP primaries, GOP candidates are appealing to Republican voters by mimicking Trump’s authoritarian assaults on the Mueller probe and the rule of law, a good indicator of what energizes the GOP base these days.

All this comes as Republicans are no longer even pretending that the GOP tax cut has the political potency that Republicans triumphally claimed it would. But that brings us to our next item.

* TAX CUT VANISHES FROM GOP MESSAGING: Reuters finds that among the most vulnerable House Republicans, there has been a remarkable dropoff in messaging about the GOP tax cut on social media, on congressional and campaign websites, and in digital ads:

All told, the number of tax messages has fallen by 44 percent since January. For several congressmen in tough reelection fights … messaging is down much more — as much as 72 percent.

The tax cut was supposed to be the GOP’s midterm savior, yet the focus is increasingly on the Mueller “witch hunt” instead. Says it all.

* GIULIANI ADMITS THERE MAY HAVE BEEN OTHER PAYMENTS: On ABC’s “This Week,” Giuliani was asked whether Trump lawyer Michael Cohen might have made “payments to other women for the president” in addition to the Stormy Daniels hush-money payment. He replied:

“I have no knowledge of that but I would think if it was necessary, yes. He made payments for the president, or he conducted business for the president, which means he had legal fees, monies laid out, and expenditures, which I have on my bills to my clients.”

Yeesh, you’d think a crack lawyer like Giuliani would have made it his business to inform himself of little details such as this one.

* STORMY DANIELS’S LAWYER CLAIMS PROOF OF TRUMP LYING: Also on “This Week,” Stormy’s lawyer Michael Avenatti was asked whether he has proof that Trump knew about the hush-money payment at the time. He replied:

“We have evidence that the president knew in the months at least following the campaign of this payment, certainly knew it long before his statement on Air Force One in April of this year where he effectively stood there and lied to the American people about not knowing anything about this payment.”

This would mean Trump agreed to reimburse Michael Cohen while also knowing what he was reimbursing him for, despite saying otherwise. If so, this evidence should come out at trial.

* KELLYANNE CONWAY’S ADMISSION: On CNN’s “State of the Union,” counselor to the president Kellyanne Conway was pressed on Trump’s claim on Air Force One that he didn’t know about the payment, and she said:

“In speaking with the president just yesterday, when the president said no on Air Force One, he was talking about he didn’t know when the payment occurred. … I’m going to relay to you what the president has told me, which is the best I can do. He didn’t know it at the time that the payment occurred.”

Their line is now that when Trump said he didn’t know about the payment, he actually did know about it, and was referring to whether he knew about it when it was made. That suggests Avenatti could be right.

* GIULIANI IS CERTAIN THINGS ARE GOING GREAT: Giuliani tells The Post that his media tour is going swimmingly:

“We all feel pretty good that we’ve got everything kind of straightened out and we’re setting the agenda … Everybody’s reacting to us now, and I feel good about that because that’s what I came in to do.”

Well, if nothing else, this transparently absurd bluster shows that Giuliani knows his audience (of one, that is).

* MUELLER FACES A CALENDAR PROBLEM: The Wall Street Journal reports that many experts think Robert S. Mueller III will have to go quiet in the run-up to the midterm elections, to avoid perceptions that he’s trying to influence them:

Though Mr. Mueller doesn’t face any specific legal deadline, the fall midterms amount to a political one, according to experts and prosecutors. He will reach a point this summer when Justice Department habits dictate he would have to go dark so he doesn’t appear to be trying to sway voters’ decisions … Any action by Mr. Mueller … could play into whether Democrats take control of one or both houses of Congress.

You will recall, of course, that former FBI director James B. Comey intervened twice during the 2016 election and that Trump and Republicans widely exploited that both times.

* HOW REPUBLICANS SUCCEED IN TRUMP ERA: Politico reports that four House Republicans have become big GOP players by leading the charge against the Mueller probe:

They have demanded thousands of documents central to special counsel Robert Mueller’s investigation. … This crew of hard-charging conservatives … have emerged as some of Washington’s most prominent Republicans, enjoying direct lines to the Trump White House and flights on Air Force One. … None of the four holds a powerful committee chairmanship, but they have something just as important: regular airtime on Fox News.

Running a 24/7 assault on the rule of law appears to be the route to Republican superstardom these days.