Conservative Republicans were mighty upset when their party nominated Richard Nixon in 1960. Nixon was supposed to be a conservative, but his nomination had begun to look like a sellout to the party’s liberal wing. That’s when Barry Goldwater strode to the podium and administered a slap. “Grow up, conservatives,” he told them.

That’s what some conservatives need to hear today. They’re not happy Steve Bannon has left the White House. And they hate the planned troop increase in Afghanistan. They need to grow up.

They need to chill.

First, let’s remember that Bannon fired himself. He didn’t just quit, he slammed the door on his way out. Second, those of us who voted for President Trump did so because we had liked what he was saying long before Bannon came on the scene.

That includes Trump’s foreign-policy speech in April 2016. I really, really liked that one. It was well-reasoned, astute and sensible. Heck, it was brilliant. And I’d think so even if I hadn’t had a hand in drafting it.

Here’s what Trump said about ISIS: “I have a simple message for them. Their days are numbered. I won’t tell them where and I won’t tell them how.” He said exactly the same thing Monday night. “I will not say when we are going to attack, but attack we will.”

Right now, the principal breeding ground of Islamic jihadism is Afghanistan, not Syria, and Trump correctly concluded that the best way to prevent another 9/11 is to continue the fight in that country. It’s just what he promised on the campaign trail.

Now, let’s be clear about what Trump didn’t do or say on Monday. He didn’t say we should cut and run, as President Barack Obama did with a drastic withdrawal of US forces in Iraq that gave us the Islamic insurgency in that country and killed many thousands of people. The Bannonites seem to think that somewhere along the line, Trump promised he’d withdraw all US forces around the globe. He didn’t.

Trump also didn’t say that he wanted to continue our failed strategy of nation-building. Back in 2016, he said, “We’re getting out of the nation-building business and instead focusing on creating stability in the world.”

And as he told us Monday night, the litmus test is going to be our national interest. We’re not going to try to make a democracy out of Afghanistan. Trump even extended a cautious hand to the Taliban: “We are a partner and a friend, but we will not dictate to the Afghan people how to live or how to govern their own complex society. We are not nation-building again. We are killing terrorists.”

Trump said that we need to be flexible, so as not to give the game away to our enemies — just as he said during the campaign: “We must as a nation be more unpredictable. We are totally predictable. We tell everything. We’re sending troops. We tell them.”

And he said the same thing Monday: “We will not talk about numbers of troops or our plans for further military activities. Conditions on the ground, not arbitrary timetables, will guide our strategy from now on. America’s enemies must never know our plans or believe they can wait us out.”

It’s reported that we’re going to increase our troop levels in Afghanistan from the present 10,500 to about 15,000. True to his word, Trump didn’t mention numbers in the speech. A senior White House spokesman, however, told me that the number in question will be in the low five-figure range.

It won’t be the major surge of 30,000 or 40,000 troops that some had imagined. Instead, we’re going to rely on the Afghan army to do the combat fighting while supporting them largely with air power. As Trump said last night, “Ultimately, it is up to the people of Afghanistan to take ownership of their future.”

Finally, Trump announced that he expects our NATO allies to step up to the plate in the fight. They had no reason to do so when Obama was president, when there was no strategy for victory and when we let them free ride on us. But there’s a new sheriff in town.

Bannon’s dismissal, then, is irrelevant here. President Trump is doing just what candidate Trump promised a year ago.

F.H. Buckley is a professor at Scalia Law School at George Mason University and author of “The Way Back: Restoring the Promise of America.”