For Democrats, Joe Biden is the incumbent president, and his candidacy is all but assured.

So Super Tuesday simply brings him one step closer to being announced as the nominee at the party’s convention in the middle of the year.

Fifteen states – including California and Texas – take part

Alabama, Alaska, Arkansas, California, Colorado, Maine, Massachusetts, Minnesota, North Carolina, Oklahoma, Tennessee, Texas, Utah, Vermont, Virginia and the US territory of American Samoa.

States worth watching include California and Texas, which are the nation’s most populous states and therefore have the greatest share of delegates to award (169 and 161, respectively).

Colorado could be interesting, as it’s the state that attempted to remove Trump from the ballot by arguing he incited an insurrection and therefore was ineligible for office.

Alabama has also become a political flashpoint after its Supreme Court ruled that frozen embryos should be considered as children, meaning people could potentially be sued if they were destroyed.

However, of the 15 states, the only major battleground for the general election in November is North Carolina, as the rest are expected to fall solidly to the Democrats or Republicans.

Trump narrowly won North Carolina against Biden in 2020, but Democrats view the state as attainable given the shifting demographics in fast-growing areas around Charlotte and Raleigh.

Loading

In a sign of how high the stakes are, both Trump and Haley headed to North Carolina for rallies over the weekend.

Vice President Kamala Harris also visited the state to announce a $US32 million ($49 million) investment for small businesses and to discuss the administration’s economic successes in the area.

Trump will inch closer to the nomination

Trump won’t be able to sew up the nomination, but he will certainly be close. The Trump campaign believes the former president will likely have the 1215 delegates he needs to secure the nomination by mid-March.

Apart from Haley’s first primary win in the District of Columbia this week, Trump has won all the nominating contests so far.

His winning streak began with the Iowa caucuses in January (where he beat a slightly more crowded field that also included Florida Governor Ron DeSantis and biotech entrepreneur Vivek Ramaswamy) followed by victories in New Hampshire, Nevada and Haley’s home state of South Carolina last month.

On Saturday, he clocked up three more wins at the Missouri, Michigan and Idaho Republican caucuses.

He now has 244 delegates nationwide, while Haley has 43.

Nikki Haley’s commitment

Haley’s victory in the progressive electorate of Washington DC gave her campaign a much-needed boost, but she still faces an almost insurmountable battle to beat Trump.

Nonetheless, the former UN ambassador has committed to campaigning to at least the end of Super Tuesday, making the case that Trump and Biden are “two old men who are only getting older” and Americans deserve a “new generational leader” to unite the country.

While there does not appear to be a path to victory for Haley, she could at least be competitive in some of the more moderate states, such as Virginia, Vermont, and Maine.

By resisting the pressure to drop out, she has also propped up her viability as a possible presidential candidate in 2028 or as the alternative for Republicans if something were to happen to Trump and he can’t run in November.

Loading

Democratic longshots

Biden has two longshot rivals also vying for the Democratic nomination: Minnesota Congressman Dean Phillips and self-help guru Marianne Williamson (who took the unusual step of suspending her campaign a few weeks ago, only to unsuspend it after the Michigan primary race).

Both, however, are polling under 3 per cent and have little chance of winning.

In the absence of a genuine rival, Biden’s challenge really relates to the general election in November. At 81, he is already America’s oldest president and faces lingering concerns about his mental acuity and ability to do the job for another four years.

He has also suffered record-low approval ratings, and issues such as the crisis at the US-Mexico border, the war in Gaza, and the US economy remain a challenge.

What’s more, the coalition he needs to win back the White House is fraying. This was evident in the Michigan primary race, where Arab-Americans, young people and progressives mounted a grassroots campaign encouraging people to vote “uncommitted” in the Democratic primary race to send a message to the White House.

In a warning sign for the president, more than 100,000 people did that, with many of the biggest protest votes recorded at polling booths.

Get a note directly from our foreign correspondents on what’s making headlines around the world. Sign up for the weekly What in the World newsletter here.