National Harbor (United States) (AFP) - Former US president Donald Trump and his one-time ally Nikki Haley are to give dueling addresses this week as thousands of conservatives gather outside Washington to vet Republican hopefuls weighing bids for the White House.

A national showcase for established big hitters and rising stars alike, the four-day Conservative Political Action Conference (CPAC) starting Wednesday bills itself as the "largest and most influential gathering of conservatives in the world."

An array of right-wing A-listers -- including Brazil's recently defeated leader Jair Bolsonaro -- are expected to address the convention, although many potential 2024 candidates are staying away.

Trump's keynote speech on Saturday is likely to reprise the "Make America Great Again" (MAGA) agenda that swept him to power in 2016, taking in border security, gun rights, "woke" indoctrination and other "red meat" conservative issues.

Haley, Trump's former UN ambassador, is expected to make the case that the "Grand Old Party" (GOP) needs a new generation of leaders, unencumbered by the taint of recent election failure and able to inspire new voters as well as turning out the base.

'Balancing act'

"Nikki Haley has to negotiate the very thin line between differentiating herself from Donald Trump and still appealing to -- or not alienating herself from -- his supporters, who still constitute the vast majority of CPAC activists and GOP primary participants," said Margaret Susan Thompson, a politics and history professor at Syracuse University.

"This is a challenging balancing act, indeed. So far, she seems to be focusing on age but, given the older-skewing GOP/MAGA base, she needs to be very careful here."

Trump declared his candidacy three months before Haley's mid-February launch but his campaign has been criticized for inertia, lack of a clear political vision and the constant drip-drip of scandal.

The maelstrom of controversy encircling the former president -- from poor performances of major Trump-backed candidates to multiple investigations closing in on him -- has raised questions over his viability as a Republican totem.

"So far, most of his rallies and speeches have looked backward, focusing on the 'stolen election' and so on, rather than on what he intends to do in the future," said Thompson.

"In my view, it is not a way to expand his base of support."

Nevertheless Trump's persistent polling strength has confounded his critics and he remains the comfortable frontrunner, towering over rivals like Florida Governor Ron DeSantis and former vice president Mike Pence.

No DeSantis, or Pence

CPAC delegates will hear from more than 100 mostly pro-Trump speakers, including former cabinet secretaries, several Republican senators and numerous far right members of the House of Representatives.

But much of the party firmament, including DeSantis, Pence and the congressional and national committee leaders, are declining to make the pilgrimage to the National Harbor.

"DeSantis is stiffing CPAC because he knows Trump owns the space," said Rick Wilson of the Lincoln Project, a group of anti-Trump conservatives who claim a share of the credit for the Republican leader's defeat in 2020.

The absence of many big names comes in the wake of CPAC organizer Matt Schlapp recently denying allegations of sexual battery against a Republican campaign staffer in Georgia.

The conference traditionally ends with a "straw poll" of attendees' preferences for the Republican presidential nomination.

Trump has won every one of the unofficial surveys conducted since his 2016 election, picking up 69 percent of the vote last year, against just 24 percent for runner-up DeSantis.

"The rabid MAGA base that floods these grievance galas are Trump diehards to a tee," Wilson added.

"Just look at the straw polls that are coming out of these events. Trump couldn't get stronger support if he polled his own family."