It goes a long way to explain the tussle raging within the GOP itself -- over the party's approach to validating its Washington majority, its responsibility for global stewardship and its prospects in the 2018 midterm elections.
Trump reignited the clash Tuesday, saying on Twitter that "Liddle' Bob Corker" had been made to "sound a fool" in an interview recorded by The New York Times.
"That's what I am dealing with," he wrote.
The first is that there are now effectively two Republican parties -- one dominated by Trump and his uber-loyal followers, for whom his feud with Corker represents exactly the kind of disruption they hoped to see him unleash. The other GOP, meanwhile, is made up of establishment, orthodox conservatives like the Tennessee senator and his Majority Leader Mitch McConnell, who want to use their power to legislate and fret about Trump's global leadership.
The second rule of last year's Republican primary circus is one that Corker is now daring to confound -- namely that no one who gets down in the muck with a brutal political street-fighter like Trump comes out clean or unscathed. Trump's showdown with Corker, which went nuclear over the weekend, will go a long way to deciding the state of the GOP as it musters for midterm elections next year -- at which its monopoly in Washington will be on the line.
It could also show whether Trump's go-to tactic of waging war on the Republican Party establishment, that has proven so profitable in the past, is a viable strategy going forward or whether it is ultimately self-defeating. Trump briefly toed the party line in backing Alabama Sen. Luther Strange in his losing primary race against Roy Moore last month -- but even before voters went to the polls, he admitted he might have done the wrong thing.
In many ways, the Corker vs. Trump prizefight is familiar: it's a reprise of the classic showdown between the populist, nationalist President and a GOP grandee devoted to conservative rule at home and internationalism abroad.
"There is a lot going on in the Republican Party," Andre Bauer, a former lieutenant governor of South Carolina, told CNN's Brooke Baldwin Monday. "You have an establishment class senator in Bob Corker that has always held himself above the fray, conducted himself (as) most Republicans think a Republican senator should act like."
"But Donald Trump challenged the Republican establishment -- there are a lot of Republicans like me that quite frankly were sick of the same old, same old ... he has continued to fight the system," Bauer added.
There have been signs that if Trump fails to secure results on Capitol Hill, he could effectively become the first sitting Republican president to run against a do-nothing Congress of his own party in the midterms, perhaps by backing insurgent GOPers in primary races against establishment lawmakers.
And from the party's grassroots, Corker's intervention may seem less consequential than it did in Washington, which was transfixed by the spat that culminated when the senator warned Trump's volatile temperament could put the US on the path to "World War III."
Some Washington pundits and media commentators praised Corker for having the courage to finally stand up to Trump, for voicing what many GOP figures say privately and for no longer appeasing what they see as the President's dangerous approach to crises like the standoff with North Korea.
The base reacts
But outside Washington, things often appear differently.
Conservative talk show host Rush Limbaugh
, for instance, told his listeners on Monday that Corker was part of a cabal of Washington Republicans who wanted to "nullify" Trump and preserve the "current world order." Republican National Committee Chairwoman Ronna Romney McDaniel told CNN's Wolf Blitzer that Trump was channeling frustration against the Washington GOP's struggles to implement his agenda.
"'We sent you there, we gave you the White House, the Senate, we want to see these things get done,'" she said, voicing complaints she had heard at town hall meetings.
CNN's White House team reported Monday
that Trump was not yet done with the controversy. Sources said the President believed that other senators may be loath to criticize him, since unlike Corker, who has announced he will retire after the midterm elections, they may fear the wrath of his loyalists in primaries.
Texas Republican consultant Bill Miller described the reaction to Trump's latest antics in the Lone Star State as "eye-rolling" compared to the "head-exploding" reactions taking place in Washington. But he also challenged the perception that the President's behavior would always be accepted by grassroots Republican voters.
"This is what he does, it is a trick to do this. It works less effectively every successive time. What I believe is happening even down here in Texas, which is very conservative, is that there is a sense of a behavioral issue ... it is impolitic," Miller said. "It's just not smart. It's counterproductive, it isn't producing any kind of result you want. If your goal is to blow things up, destroy, great, but that is not a good first-term record."
Trump vs. the establishment, again
Trump has a history of taking on GOP establishment figures and crushing them, starting with the presidential primary race. When elite opponents like Jeb Bush and Marco Rubio tried to slug out a bare-knuckle fight with him, they limped away with their political reputations wounded.
But in Washington, the President's record for knockouts has been less effective. Trump's unpredictable ways and tendency to turn upon Republicans has contributed to his struggle to secure a major legislative win. His efforts to help repeal Obamacare, for instance, often seemed ill-informed or counterproductive.
And when Republican Sen. John McCain stood up to Trump's power and helped derail a last ditch bid to repeal Obamacare
, he polished his own legacy -- at least in Washington -- and won sympathy when the President attacked him shortly after his brain cancer diagnosis.
On Monday, many Beltway strategists and senior Republicans were left shaking their heads, warning that Trump's reflexive lashing out could cost him the crucial vote of Corker as he seeks a year-end legislative victory.
"Going after a senator whose vote you need on tax reform is not the best strategy," Wisconsin Rep. Sean Duffy said on CNN
But there were also signs on Monday that Washington's GOP divides may be bridgeable, as another Republican, South Carolina Sen. Lindsey Graham, who has often clashed with the President, took to the links alongside him.
Unusually, the White House allowed cameras to record Trump on the golf course, sending a message that Corker's revolt was not uniform among GOP senators. Less than two months ago, Graham was castigating the President over his sluggish condemnation of white supremacists after racial violence in Charlottesville, Virginia, warning "history is watching us all."
On Monday, after a round at Trump's club in Virginia, Graham praised him for a performance worthy of a golf pro, shrewdly identifying the way to his host's heart.
"President Trump shot a 73 in windy and wet conditions!" Graham tweeted.