President Obama. (Susan Walsh/AP)

A visibly irritated President Obama slammed Donald Trump and the broader Republican Party on Tuesday for their criticism of his unwillingness to say that the United States is at war with radical Islam, casting it as a cheap political stunt unworthy of the country.

"What exactly would using this label accomplish," Obama asked angrily. "What exactly would it change? Would it make ISIL less committed to try to kill Americans? Would it bring in more allies? Is there a military strategy that is served by this? The answer is none of the above. Calling a threat by a different name does not make it go away. This is a political distraction." ISIL is an alternative acronym for the Islamic State militant group.

[President Obama’s remarks after National Security Council meeting on Islamic State]

Why did Trump's attack get so under the skin of the usually calm, cool and collected president? Two reasons: 1) Obama believes Trump's rhetoric in the wake of this weekend's mass shooting in Orlando is not only wrong but deeply irresponsible for someone who could be president in six months and 2) Obama h-a-t-e-s the idea of doing and saying things purely for the sake of politics without any sort of deeper strategy behind them.

Let's take those issues in order.

This tweet from Tommy Vietor, a former national security spokesman for Obama, about why the president was so mad nicely captures Obama's mind-set.

If you cut through all of Obama's rhetoric in the speech today, what you get is this: Being president isn't anything like running for president. And now that Trump is one of two people who might actually be president come 2017, his words have far more meaning and impact.

Again, Obama:

This argument of labels has mostly just been partisan rhetoric, and, sadly, we have all become accustomed to that kind of partisanship, even when it involves the fight against these extremist groups.

That kind of yapping has not prevented folks across the government from doing their jobs, from sacrificing and working really hard to protect the American people.

But we are now seeing how dangerous this kind of mind-set and this kind of thinking can be. We are starting to see where this kind of rhetoric and loose talk and sloppiness about who exactly we are fighting, where this can lead us.

Wake up people, Obama is saying. Trump might be president. For real. "We now have proposals from the presumptive Republican nominee for president of the United States to bar all Muslims from immigrating into America," Obama said. "Where does this stop....Are we going to start treating all Muslim Americans differently? Are we going to start subjecting them to special surveillance? Are we going to start discriminating against them because of their faith?"

Then there is the fact that Obama always has hated some of the accepted rules of how politics work. If you like him, you ascribe that resistance to a principled stand against fakery and coverage that puts too much emphasis on who's up and who's down. If you don't, you see it as yet another example of his arrogance and stubbornness.

Yes, it would have been somewhat easier for Obama — politically speaking — if he had simply, a few years back, used the phrase "radical Islam." But he didn't believe it then and doesn't believe it now. And, so, he wouldn't say it — or be bullied into saying it.

"There has not been a moment in my 7.5 years as president where we have not been able to pursue a strategy because we didn't use the label 'radical Islam,'" Obama steamed. "Not once has an adviser of mine said, 'Man, if we use that phrase, we are going to turn this whole thing around.' Not once."

Obama prides himself on that refusal to bow. That separates him from Hillary Clinton, who tends to be more willing to jump through political hoops — even if she thinks it's dumb. Witness her shift over the past 48 hours on saying the words "radical Islam."

Add it all up and you get a very pissed-off Obama. Pissed off about the fact that Trump has gotten as far as he has given what he says about the challenges facing the country. Pissed off over the idea that saying or not saying two words can be regarded as making any difference in the threat posed by the Islamic State. Pissed off — maybe — that he can't run directly against Trump and expose the real estate mogul for his rhetoric.

Just plain pissed off. Which is a rare state to catch Obama in. Trump tends to have that effect on people.