First Read is a morning briefing from Meet the Press and the NBC Political Unit on the day's most important political stories and why they matter.

Has Trump already conquered the Republican Party?

It’s more than a legitimate question to ask, especially after the results from our new NBC/WSJ poll and after last night’s GOP debate. Let’s start with the poll: Not only has Trump more than doubled his national lead -- from five points to 13 -- two-thirds of GOP primary voters (65%) say they could see themselves supporting him. That’s up from just 23% who said this back in March.

What’s more, in hypothetical one-on-one match-ups, Trump tops Rubio, 52%-45%, though he loses to Cruz, 51%-43%. And in a three-way race, it’s Trump 40%, Cruz 31%, and Rubio 26%. So the combined outsider/insurgent wing is at 71%, while the establishment wing is at 26%. Then at last night’s GOP debate, we noticed three developments: 1) Trump has improved as a debater (his response to “New York values”; 2) his antagonists like Jeb Bush have been reduced to asking him to merely “reconsider” (!!!) his Muslim ban proposal; and 3) a cheerful optimist like Marco Rubio has turned much gloomier, suggesting Trump’s influence on the race has even trickled down to the Florida senator. Maybe most amazing of all are these recent tweets that New York Magazine’s Jonathan Chait compiled from prominent Republicans/conservatives:

@RichLowry: From my convos, GOP estab mood on Trump moving from fear/loathing to resignation/rationalization,ie he'd run better than cruz & slam Hillary

@mattlewis: Same source (when I ask what's happening on the ground): "On the ground? Everyone literally is getting resigned to Trump as nominee."

@AriFleischer: Trump was Trump and that means he had a good night. I give him a 60% shot of being the GOP nominee.

You know the different stages of grief -- shock and denial, pain and guilt, anger and bargaining. Well, have we finally reached the last stage, acceptance? Now none of this means that Trump is going to win the GOP presidential nomination. But it does mean that he’s become much more acceptable to Republicans than we ever thought possible; that he’s indelibly shaped the GOP contest in his own image; and that he’s in firm control of this GOP race.

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As for last night’s debate, it reinforced the findings of our poll: The three Republicans who dominated in terms of presence were Trump, Cruz, and Rubio, while Chris Christie and Jeb Bush didn’t have much of a target on their backs. Other observations: It was, by far, Trump’s best debate performance; we saw Cruz on the defensive more than we’ve seen in any other debate; and Rubio had an uneven outing, under performing (surprisingly) in the early portion and excelling later on (in his clash with Cruz over immigration, etc.).

Lindsey Graham endorses Bush

Breaking news this morning: Lindsey Graham is going to endorse Jeb Bush. And Bush appeared on “Fox News” this morning to trumpet the endorsement, NBC’s Hallie Jackson reports. "His endorsement is very meaningful." Bush said. “Along with it come friends and supporters of his, so I'm excited about it.” It’s a sign of the GOP establishment consolidating. But a warning: As that three-way hypothetical result from our NBC/WSJ poll shows -- with Trump at 40%, Cruz at 31%, and Rubio at 26% -- the establishment side isn’t where the energy is in the Republican Party right now. That said, the endorsement will breathe some much-needed life into the Bush campaign for the next 24 hours.

Continuity vs. Revolution and the fight over the heart and soul of the Democratic Party

Turning to the Democratic race, Sunday night brings us the final Dem debate before the Iowa caucuses -- moderated by NBC’s Lester Holt and NBC’s Andrea Mitchell from Charleston, SC -- and it promises to be a doozy. Not only do we have a neck-and-neck race in Iowa, but we have a true fight over the heart and soul of the Democratic Party. Do Democrats go with the candidate essentially running on continuity with President Obama (Hillary Clinton), or do they back the candidate promising revolution (Bernie Sanders)? Should their nominee be another Clinton? Or should it be a self-avowed democratic socialist who hasn’t been a member of the party until now? We’ve spent so much time looking at the establishment-vs.-insurgent divide inside the Republican Party, but don’t dismiss the equally compelling fight within the Democratic Party over where it should be entering Year 8 of the Obama presidency.

Team Hillary still hasn’t figured out a way to go after Bernie

Meanwhile, yesterday’s conference call by the Clinton campaign blasting Sanders over his contrast TV ad suggests that Team Hillary still hasn’t quite figured out how to go after Sanders. Is it portraying him as a politics-as-usual politician? An untested Vermonter who has no idea what the GOP has in store for him if he’s the nominee? An independent who’s disloyal to Obama (on Obamacare, Dodd-Frank)? Bottom line: It seems the Clinton campaign is throwing a lot of things against the wall to see what sticks -- maybe because it never thought it would be in this position.

Recapping Clinton’s interview with Rachel Maddow

In Clinton’s interview with MSNBC’s Rachel Maddow last night, it seemed Clinton tried a couple of those approaches vs. Sanders. “Obviously Sen. Sanders has said repeatedly he doesn’t do that, he doesn’t you know engage in negative attacks. And I take him at his word. Anything personal, we don’t do that in our side of the debates,” Clinton said. “I mean basically [his new TV is] also a very direct criticism of President Obama who, as you might recall, took a lot of money from the financial industry when he ran in 2008. That didn’t stop him from fighting for the hardest regulations on Wall Street since the Great Depression.” More Clinton: “So the voters have been led to believe that before they go make their decision, they’ll be able to compare what I want to do to get to universal care, which is to defend, support and enhance the Affordable Care Act. And what Sen. Sanders has said he wants to do, which is to basically start all over again, start a contentious debate to try to get to a single payer system. But he’s not telling us what it will look like and what it will cost.”

On “Meet” this Sunday: Bernie and Jeb: Appearing on “Meet the Press” this Sunday will be Jeb Bush and Bernie Sanders.

On the trail: Donald Trump spends his day in Iowa… So does Bill Clinton, who holds three events in the state… Marco Rubio is in New Hampshire, where he makes four stops… Ted Cruz and Ben Carson remain in South Carolina after last night’s debate… Jeb Bush, John Kasich, Carly Fiorina, and Rand Paul are all in New Hampshire… And Mike Huckabee is in South Carolina, while Martin O’Malley hits Iowa.

Countdown to NBC/YouTube debate in SC: 2 days

Countdown to Iowa: 17 days

Countdown to New Hampshire: 25 days

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