Washington (AFP) - Donald Trump hits the campaign trail Saturday for the first time in a stuttering third bid for the US presidency overshadowed by intensifying criminal investigations and a firestorm of political controversy.

The twice-impeached Republican, whose party lost the White House and both chambers of Congress during his term, makes his case for another four years with appearances in New Hampshire and South Carolina.

Some 650 days ahead of the next election, Trump remains the Republican frontrunner, but his grip on the rank-and-file has loosened during his two years in the wilderness since exiting the Oval Office.

"Mr Trump's conduct since announcing his candidacy for the 2024 Republican nomination has weakened his credibility within his party," Brookings Institution senior fellow William Galston said in a recent commentary.

The 76-year-old Trump has been unusually low-key since announcing his latest presidential run on November 15, cocooned at his Mar-a-Lago beach home in south Florida and declining to hold a single public event.

But he heads onto the stump facing simmering discontent over midterm elections that saw a series of extremist candidates he had backed rejected in crucial battleground states.

The former reality TV star also has riled establishment Republicans over a dinner he hosted in Florida with a notorious Holocaust denier and the anti-Semitic, Hitler-admiring rapper formerly known as Kanye West.

His continued election denialism and a call in December for the termination of the Constitution to reinstate him to office also sparked a chorus of opprobrium.

'Narrow path'

Trump will address Republicans in the New Hampshire commercial hub of Salem on Saturday morning, before leading a rally in South Carolina's capital, Columbia.

His first two locations are no accident: the states hold outsize influence as two of the first in every presidential election year to hold nominating contests -- known as "primaries" or "caucuses," depending on local custom.

Both cemented Trump's frontrunner status in 2016 after a lukewarm start while South Carolina rescued Democratic President Joe Biden's floundering campaign in 2020.

In Congress and around the country, some Republicans are openly suggesting the party is ready for a younger, fresher face -- someone who is less polarizing and unencumbered by the constant drip of scandal.

Two South Carolina Republicans in their 50s -- Senator Tim Scott and former governor Nikki Haley -- are believed to be eyeing potential presidential runs, and neither is expected to show up on Saturday.

Galston said while Trump still has a "narrow path" to victory in 2024, the former president was "increasingly seen as a loser -- and rightly so" after the midterms.

But the battle for the nomination could wind up a two-horse race between Trump and Florida Governor Ron DeSantis, who would be unlikely to announce until after the Sunshine State's legislative session ends in May.

If DeSantis does run, he will be hoping for a more successful launch than Trump, who saw no polling bump after his November announcement.

Hush money

Mounting legal woes still appear however to be the biggest roadblock for Trump, whose company was convicted on 17 counts of tax fraud and related offenses the week before he announced his run.

He is facing criminal probes in Atlanta and New York over election interference allegations and a hush money payment to a porn star. 

Federal prosecutors are scrutinizing his handling of misappropriated government secrets, his role in the 2021 assault on the US Capitol and his attempts to overturn his election defeat.

He is also defending lawsuits in New York over a mid-1990s rape accusation and an alleged fraud that misled lenders, insurers and tax authorities over a period of years.

But counting out the perennial comeback kid could yet prove to be a mistake, say those who point to the success of Trump's brand as an insurgent who doesn't play by the rules.

Political scientist Jeff Broxmeyer told AFP that while the midterms had likely eroded Trump's mainstream support, his scandals had done him little harm among his base.

"Perpetual legal suits and coalition building with far-right figures are central features of Trump's appeal to Republican primary voters -- not obstacles to it," the University of Toledo professor said.