President Trump was booed when he gave a long, angry speech in Phoenix; he was cheered when he vowed to continue a long, futile war in Afghanistan.

These two facts say a great deal about our current political climate. They also explain why Trump's decision to stay in Afghanistan — come hell or Blackwater, says former Bush 41 defense official Jed Babbin — was the only one he was ever likely to make.

If there is a consistent theme to the wars the United States has fought over the last 16 years, it is this: non-nuclear-armed rogue regimes that find themselves in American crosshairs quickly come to an end, but all the president's horses and all the president's men cannot put Humpty back together again.

That is what happened after the overthrow of Saddam Hussein in Iraq. It happened after we came, we saw and Moammar Gadhafi died in Libya. And it is what we are still struggling with 16 years after toppling the Taliban in Afghanistan.

This history is undoubtedly what Trump had in mind when he told the American people, "We are not nation-building again. We are killing terrorists."

Famous last words.

During the campaign, Trump criticized both George W. Bush and Barack Obama, his two immediate predecessors, for their conduct in Iraq. He zinged Bush for going to war in the first place — a "big, fat mistake," Trump said — and Obama for withdrawing too quickly.

For a time, it seemed that Trump would extend his specific criticism of Bush's decision to invade Iraq into a more general skepticism of regime change in the Middle East. Dethroning relatively secular dictators, no matter how horrible they may be, leads to chaos and jihadism, he said.

On Monday night, Trump leaned heavier on where he found fault with Obama. "[I]n 2011, America hastily and mistakenly withdrew from Iraq," he said. "As a result, our hard-won gains slipped back into the hands of terrorist enemies. Our soldiers watched as cities they had fought for, and bled to liberate, and won, were occupied by a terrorist group called ISIS."

"The vacuum we created by leaving too soon gave safe haven for ISIS to spread, to grow, recruit, and launch attacks," Trump argued. "We cannot repeat in Afghanistan the mistake our leaders made in Iraq."

Here are the stakes as Trump sees them: "A hasty withdrawal would create a vacuum that terrorists, including ISIS and al Qaeda, would instantly fill, just as happened before Sept. 11th."

Then there are the domestic political considerations. It can't be lost on Trump that some of the Republicans who were most concerned by his reaction to Charlottesville and who are most likely to turn on him in any controversy were among the most effusive in their praise of his Afghanistan policy.

Sen. John McCain, R-Ariz., credited Trump with "moving us well beyond the prior administration's failed strategy of merely postponing defeat."

"I am very pleased with this plan and I am very proud of my president," said Sen. Lindsey Graham, R-S.C. He lauded Trump's "smarts and moral courage."

Sen. Marco Rubio, R-Fla., praised Trump's speech as "excellent" and the new Afghanistan strategy as "very good."

Trump won the White House without most of these lawmakers — only Rubio was an endorser on Election Day — and didn't hesitate to take thinly veiled shots at McCain in his home state Tuesday night. But with the trajectory of the Russia probe and the paucity of majority legislative achievements to date, they could emerge as an important constituency for Trump on Capitol Hill.

No matter how far Trump goes in alienating them, it seems that all he needs is a more hawkish stand on Afghanistan, Syria or wherever to reel them back in.

The problem is that Trump hasn't severed the link between nation-building and killing terrorists. He hasn't reoriented U.S. policy toward our recent successes (defeating clear-cut enemies) and away from our recent failures (replacing them with states that can function without our help).

We enter foreign countries, then justify our indefinite presence in them, to keep their citizens from killing Americans. But we end up fighting primarily to keep them from killing each other. The "conditions" on the ground that would enable our fighters to ever leave seem no closer than a decade ago.

That may sound more like a "blank check" to Afghanistan than Trumpian "America first." But it just might stop the booing for a while. That instinct is harder for Trump not to follow.