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.

Trump's GOP takeover is now complete

On March 3, Mitt Romney delivered his own blistering speech on Donald Trump, which used some of the same lines of attack that Hillary Clinton included in her anti-Trump address yesterday. “[Trump’s] domestic policies would lead to recession. His foreign policies would make America and the world less safe. He has neither the temperament nor the judgment to be president and his personal qualities would mean that America would cease to be a shining city on a hill,” Romney said back then. But today — exactly three months ago since that speech — Trump's takeover of the Republican Party is now complete, especially after House Speaker Paul Ryan (Romney's 2012 running mate) endorsed the real-estate mogul. Ryan tried to give himself distance by withholding his endorsement for 29 days after Trump became the GOP’s presumptive nominee, particularly given their differences over immigration, entitlements, trade, and Trump’s Muslim ban. But it’s hard to disagree with this take from the Cook Political Report’s David Wasserman: “Speaker Paul Ryan endorses nominee who wants to ban Muslims from the country. The hostile takeover of the GOP is now complete.”

But are Republicans like Ryan SINOs -- Supporters In Name Only?

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But there’s another side to a hostile takeover: Your new allies aren’t necessarily going to be the strongest backers. For example, take yesterday’s tough speech by Hillary Clinton (more on that below). While it seemed like the entire Democratic Party was on TV promoting and emphasizing Clinton’s speech, Trump and his campaign were on an island. Yes, Sens. Jeff Session (R-AL) and Tom Cotton (R-AR) issued statements criticizing Clinton, but that was it. And that’s one way to view the Paul Ryans of the world: There are going to be SINOs -- Supporters In Name Only. But when the going gets tough, as happens in all campaigns, will the entire Republican Party get behind Trump? That’s a real question right now. Sure, they’re not going to vote for Clinton. But how deeply committed are they to Trump?

Trump once again invokes “Mexican heritage” of federal judge overseeing Trump University lawsuits

The endorsement from Ryan -- who gave his own speech back in March calling for a more positive view of American politics (which many saw as a rebuke to Trump) -- came on the same day that Trump once again criticized the federal judge overseeing the Trump University lawsuits. Trump’s complaint to the Wall Street Journal: The judge is a Mexican-American. “In an interview, Mr. Trump said U.S. District Judge Gonzalo Curiel had ‘an absolute conflict’ in presiding over the litigation given that he was ‘of Mexican heritage’ and a member of a Latino lawyers’ association. Mr. Trump said the background of the judge, who was born in Indiana to Mexican immigrants, was relevant because of his campaign stance against illegal immigration and his pledge to seal the southern U.S. border. ‘I’m building a wall. It’s an inherent conflict of interest,’ Mr. Trump said.” When asked yesterday on CNN if Trump could have a Goldwater Effect with Latino voters for generations to come, Senate Majority Leader Mitch McConnell answered, “I do. I do.” Mitch McConnell -- another SINO?

Clinton delivers “toughest speech yet” hitting Trump

As for Hillary Clinton’s anti-Trump speech yesterday, it was arguably her best moment of the 2016 campaign so far (the other competitors here are her Benghazi Committee testimony and her first debate performance). Here’s the take from MSNBC’s Alex Seitz-Wald: “[O]n Thursday in San Diego, Clinton delivered what was easily her toughest speech yet on the presumptive Republican nominee, deploying a potent combination of her well-known policy wonkishness with a surprising dose of ridicule. It's too early to know for sure whether it will work, and if she becomes the Democratic nominee as expected she'll need to repeat the message a few thousand times before November for it to stick. But Clinton's performance, the latest and most effective in a series of putative "opening salvos" of the general election, was immediately hailed by Democrats as a welcomed change for a candidate who often struggles to transcend policy minutiae.” Campaigning in California last night, Trump responded to Clinton's speech. “I watched Hillary today, it was pathetic. It was pathetic.” And discussing Clinton’s emails, Trump added, “Hillary Clinton has to go to jail. OK, she has to go to jail, has to go… She's guilty as hell.”

Bernie Who?

The other takeaway from Clinton’s speech yesterday -- which was delivered in San Diego, CA -- was that it served to marginalize Bernie Sanders. Indeed, it made the Democratic primary race seem so much smaller, despite the competitive race in California. The Clinton-vs.-Sanders contest seems a lot less significant today than it did yesterday. In many ways, California voters will decide whether the Democratic race ends on June 7-8, or whether it will continue into July. And you could make the case that Clinton was trying to make this argument to California Democrats: It’s time to start the general election ASAP.

On the trail

Donald trump holds a rally in Redding, CA at 4:00 pm ET… Hillary Clinton makes four stops in California, hitting Culver City, Westminster, Santa Ana, and San Bernardino… Bernie Sanders campaigns in Fairfield, CA and Cloverdale, CA… And Bill Clinton stumps in California as well. Don’t forget to check out the political unit’s rolling minute-to-minute coverage of all the latest 2016 developments at the On the Trail liveblog at NBCNews.com.

Programming note

Due to NBC Sports programming, “Meet the Press with Chuck Todd” will air across the nation at 8 a.m. ET/ 5 a.m. PT this coming Sunday, June 5. The show may be pre-empted in some markets but will be available On Demand with video available online at MeetThePressNBC.com.