COLUMBIA, S.C. (AP) -- After a week of bitter attacks, Republicans face off Saturday in South Carolina's presidential primary, a contest that could determine Donald Trump's strength as a front-runner and help clarify whether a more mainstream politician will ever emerge to challenge him.
Democrats are holding a caucus Saturday in Nevada, the first test for Hillary Clinton and Bernie Sanders in a more racially diverse state. While Clinton's campaign once saw the Western battleground as an opportunity to start pulling away from Sanders, her team is nervously anticipating a close contest with the Vermont senator.
"We are here to win," Sanders declared Friday during a rally in sparsely populated Elko, Nevada.
For both parties, the 2016 election has revealed deep voter frustration with Washington and the influence of big money in the American political system. The public mood has upended the usual political order, leaving more traditional candidates scrambling to find their footing.
No candidate has shaken the political establishment more than Trump. He spent the week threatening one rival with a lawsuit, accusing former President George W. Bush of lying, and even tangling with Pope Francis on immigration — yet South Carolina is still seen as his state to lose in Saturday's voting.
"We have a movement going on, folks," Trump told a 5,000-person crowd in Myrtle Beach on Friday. "And we can't blow the movement. We have to make sure we get a big mandate. We have to go out tomorrow we have to go out and vote."
For Trump, a victory in South Carolina could foreshadow strong showings in the collection of Southern states that vote on March 1. Wins in those Super Tuesday contests could put the billionaire in a commanding position in the delegate count, which determines the nomination.
Texas Sen. Ted Cruz is banking on a well-regarded get-out-the-vote operation and an army of 10,000 volunteers to help overtake Trump on Saturday, as well as in the Southern states that follow. But a failure to top the real estate mogul here could puncture that strategy, though Cruz will still have more than enough money to run a long campaign.
Marco Rubio and Jeb Bush are fighting to establish themselves as credible alternatives to Trump and Cruz, candidates some GOP leaders believe are unelectable in November. While neither Bush nor Rubio expects to win South Carolina, they're battling to finish ahead of one another — with the loser in that contest likely to face tough questions about his long-term viability.
Rubio scored the endorsements of several prominent South Carolina politicians, including Gov. Nikki Haley, and seems to have rebounded after a dismal debate performance two weeks ago. Bush hopes his deep family ties to South Carolina — his brother and father each won two primaries here — will be a lifeline for his struggling campaign.
Also in the mix is Ohio Gov. John Kasich, who has low expectations in South Carolina and is hinging his White House bid on more moderate states that vote later in March, and retired neurosurgeon Ben Carson, who has a small but loyal cadre of followers.
For Democrats, the contest between Clinton and Sanders has become closer than almost anyone expected. Sanders, an avowed democratic socialist, has energized voters, particularly young people, with his impassioned calls for breaking up Wall Street banks and providing free tuition at public colleges and universities.
Clinton is hoping to offset Sanders' youth support by winning big majorities among blacks and Hispanics. She'd eyed Nevada, where one-fourth of the population is Hispanic, as the first in a series of contests that would highlight that strength.
But Clinton's campaign has been downplaying expectations in Nevada in recent days. A victory for Sanders — or even a narrow loss to Clinton— would give his campaign a boost heading into the Democratic contests on Super Tuesday.
Prognostications are difficult in Nevada, which holds a late-morning caucus. Democrats will gather at 200 caucus sites across the state, including six at Las Vegas Strip casinos so housekeepers, blackjack dealers and others with weekend schedules can attend.
Unlike in Iowa, caucuses are not a part of the political fabric of Nevada. Campaigns and parties have been holding training sessions so voters won't be intimidated by the process.
Democrats and Republicans will swap locations in the coming days. The GOP holds its caucus in Nevada on Tuesday, while Democrats face off in South Carolina on Feb. 27.