Nikki Haley will soon become the second major candidate, after former President Trump, to enter the race for the Republican Party's 2024 presidential nomination.
Haley, a former U.S. ambassador to the United Nations and former governor of South Carolina, is expected to make her campaign official at a February 15 event in Charleston.
Haley is clearly a serious candidate - but she faces big challenges.
Here are five big questions around her candidacy.
What's her appeal?
There is a lane for Haley to run in. Whether it could take her to victory is a whole other question.
In short, Haley offers a more inclusive, less abrasive version of conservatism than either Trump or Florida Gov. Ron DeSantis (R), who is widely expected to make his own run.
Part of the difference stems from Haley's biography - the daughter of Indian immigrants, she was South Carolina's first female governor. She would become the GOP's first female presidential nominee if she won.
She also has shown a capacity to address sensitive issues in a more nuanced way than Trump or DeSantis tend to do.
Perhaps her most high-profile moment on the national stage came when she backed the removal of a Confederate flag from the South Carolina statehouse grounds in 2015. She came to that position after a racist attack on a historic Black church in Charleston in which nine people were killed.
At the same time, Haley is more conservative than figures like former Maryland Gov. Larry Hogan (R) or New Hampshire Gov. Chris Sununu (R), both of whom are mulling runs but whose centrism gives them an extremely slim chance of success in today's GOP.
How strongly will she and Trump attack each other?
Trump offered new criticisms of Haley on Thursday.
"Nikki suffers from something that's a very tough thing to suffer from - she's overly ambitious," the former president told conservative radio host Hugh Hewitt.
Trump also noted in the same interview that Haley had at one stage pledged not to run in 2024 if he did so. She has clearly broken that promise.
The dynamic between Trump and Haley is a complicated one.
She had been highly reluctant to board the 'Trump Train' in 2016, initially backing Sen. Marco Rubio (R-Fla.) in his presidential bid and later switching to Sen. Ted Cruz (R-Texas).
Haley accepted Trump's offer to be United Nations ambassador and served without any public sign of dissent for almost two years. She left her post voluntarily but somewhat abruptly in late 2018 - adding to distrust of her among Trump's inner circle.
On Thursday, although Trump's criticisms were somewhat mild by his standards, his allies in the Make America Great Again PAC emailed reporters a compilation of criticisms of Haley from conservative political and media figures including former Trump strategist Steve Bannon and Tucker Carlson of Fox News.
The other question is whether Haley will bore in on Trump.
In recent months, her criticisms of Trump have been mostly implied rather than direct. At a speech to the Republican Jewish Coalition shortly after last fall's midterm elections, Haley lamented that "Republicans spent as much time fighting each other as we did the Democrats."
She added, "The truth is, Americans were not trusting the state of our party. They don't want chaos. They want strength and stability and unity."
What does her decision mean for other yet-to-declare candidates?
Haley has stolen a march on the rest of the field with her decision.
That won't matter much at all to DeSantis, who is clearly the most serious challenger to Trump based upon early polling.
Similarly, the most moderate potential candidates won't feel crowded by Haley's arrival on the scene either, as they are running in a different lane.
Her entrance into the race does make life a bit more complicated for figures like Pence and Pompeo, however.
Their appeal is broadly similar to Haley's - Trump administration veterans who are nevertheless seeking to thwart his bid for a third presidential nomination.
Haley's campaign launch doesn't at all rule Pence or Pompeo out - but it certainly doesn't help.
What if another South Carolina candidate, Sen. Tim Scott, runs?
Scott is one of the more intriguing possible 2024 contenders. Well-liked by his Senate colleagues, some Republicans think he is among the best-placed figures to unite the pro-Trump and Trump-skeptical wings of the party.
There are some doubts about whether Scott really wants the Oval Office but he is certainly stoking speculation, most recently with the announcement that he will attend a GOP event in Iowa on February 22.
Given South Carolina's own important position toward the start of the primary calendar, a Palmetto State contest featuring Trump, Haley and Scott among the candidates would be a spectacular battle.
Does she have a real shot?
Haley has real political skills. As she is fond of noting, she has never lost an election, beginning her career in the South Carolina statehouse and then winning twice in gubernatorial contests.
Skeptics who would minimize those achievements by noting the conservative lean of the state miss the point that she has also had to win against the odds in competitive primaries - the same task that now awaits her on a national level.
That being said, Haley begins, like everyone else in the field, way behind both Trump and DeSantis in the polls. An Economist/YouGov survey last month gave her just five percent support with Trump on 44 percent and DeSantis on 29 percent.
Haley has been underestimated in the past.
But she faces a serious uphill climb to the nomination.
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