Newsletter: Essential Politics: Heading into the home stretch

This was the week that Republican presidential hopefuls finally realized that their only hope of beating Donald Trump was to actually campaign against him.

On Tuesday, we’ll start finding out if their move came too late.

Good afternoon, I’m David Lauter, Washington Bureau chief. Welcome to the Friday edition of our Essential Politics newsletter, in which we look at the events of the week in the presidential campaign and highlight some particularly insightful stories.

Thursday night’s Republican debate marked a dramatic shift in the GOP campaign, as my colleagues Noah Bierman, Mike Memoli and Molly Hennessy-Fiske described in their account of the confrontations among Trump and Sens. Ted Cruz and Marco Rubio.

For more insights into the debate, check out these takeaways by Mark Z. Barabak and this analysis by Cathy Decker of the desperate tone of the Cruz and Rubio assaults.

And read this piece by Bierman about how the GOP elite has started to come to terms with the idea of Trump as their nominee.

The problem for both Cruz and Rubio -- as well as Ohio Gov. John Kasich -- is that Trump by now has built up such a base of support that they may no longer be able to catch him.

Rubio, in particular, has been the favorite of many establishment Republicans, but as Lisa Mascaro noted, he has the huge disadvantage in that even his supporters can’t name a single state he may be able to win. And, as Trump showed Friday afternoon by unveiling an endorsement from New Jersey Gov. Chris Christie, his current lead in the race gives him a tremendous advantage: He can unveil tactical maneuvers at any point to try to gain maximum publicity or squelch whatever momentum one of his rivals can generate.

A candidate needs 1,237 delegates to secure the GOP nomination. Trump currently has 64, Cruz and Rubio 17 each. With so few delegates allocated, there’s clearly time for someone to overtake the leader. But that window will close fast. By the end of vote counting on March 15, roughly 60% of the delegates will have been chosen.

Keep track of the delegate race in both parties with our Delegate Tracker, which shows where each candidate stands and where they have won support.

Cruz’s key test will come Tuesday. He needs to win handily in his home state, Texas, and across the other Southern states that dominate the day’s events. If Trump can beat him there, in primaries heavy with conservative and evangelical voters, Cruz’s path forward will disappear.

For Rubio, at least in theory, the key moment won’t come until his home state, Florida, votes on March 15. Because Florida is a winner-take-all state, victory there would give him a large cache of delegates.

Unfortunately for Rubio, Trump has led every poll taken in Florida since July -- more than 20 publicly released surveys -- and currently leads the senator by 2-1 in averages of the most recent ones. Rubio has time to catch up, but if Trump wins most of next week’s Super Tuesday contests, he’ll head into mid-March with a big head of steam.

As no less an expert than Hillary Clinton said Friday, when asked if she thought Trump would win the GOP nomination: “Yes. I mean, right now, it looks like that.”

Speaking of Clinton, she’s expected to trounce Sen. Bernie Sanders tomorrow in South Carolina. As Chris Megerian reports from the state, many working-class black voters say they know Clinton, like her and just don’t see much point in spending time thinking about Sanders.

“I got nothing against him,” 76-year-old James Brown said of Sanders. “I don’t know that much about him.”

If black voters in South Carolina stick with Clinton, as polls suggest they will, she should be well positioned for Tuesday’s primaries in other states with large percentages of African American voters, including Georgia, Alabama, Mississippi and Arkansas.

Clinton also hopes for a big night in Texas, where she has the backing not only of black leaders, but also key Latino officeholders.

There’s been a lot of talk about Clinton’s lead among Democratic superdelegates. But if she emerges from Tuesday’s voting with a significant lead in pledged delegates, that alone will make it difficult for Sanders to catch up.

You can follow along Saturday as we post live results, speeches and analysis from South Carolina on Trail Guide.

Then come back Tuesday for all the developments in the 14 states holding contests that day.

Clinton’s support from black voters comes after a campaign in which she has spoken about race in terms that go far beyond what past candidates have been willing to use, as Megerian and Evan Halper report in this piece describing the contrast between Clinton’s and Sanders’ appeals to minority voters.

Her ability to get her campaign back on an even keel also owes something to her performances in televised town halls, Decker explained in a story that examines how Clinton has used those forums to talk about herself in more personal terms.

Finally, before his departure fades into memory, read this piece by Decker and Seema Mehta about the end of Jeb Bush’s campaign. No one has done a better accounting of what Bush’s crash means to the GOP.

For coverage of Vice President Joe Biden’s speech and other news from the California Democratic Convention this weekend, visit our Essential Politics live blog.

That wraps up this week. My colleague Christina Bellantoni will be back Monday with the weekday edition of Essential Politics. Until then, keep track of all the developments in the 2016 campaign with our Trail Guide, at our politics page and on Twitter at @latimespolitics.

Send your comments, suggestions and news tips to politics@latimes.com.