By Luciana Lopez and Steve Holland
US Democratic presidential candidate Bernie Sanders will be looking in Nevada to puncture rival Hillary Clinton's argument that he is a one-note candidate whose support is limited to mostly white states.
After routing Clinton in New Hampshire and finishing a strong second in Iowa, states with nearly all-white populations, Nevada's Democratic caucuses on Saturday give Sanders his first chance to prove he can win over black and Hispanic voters and compete nationally as the race moves to states with more diverse populations.
Republicans in South Carolina also vote on Saturday in the state-by-state contest to pick nominees for the November 8 election, with opinion polls showing front-runner Donald Trump trying to solidify his spot at the top of the pack and rivals Ted Cruz and Marco Rubio fighting for a second-place finish.
Behind them, Republican candidates Jeb Bush, John Kasich and Ben Carson could be vying in South Carolina to keep their campaigns alive before the presidential race rapidly picks up steam in March when dozens of states hold nominating contests.
The long day of voting begins in South Carolina, where polls open for Republicans at 7am and close at 7pm.
Nevada's Democratic caucuses will begin at 2pm EST, with results expected to begin rolling in a few hours later.
Public opinion polling has been scarce in Nevada, where Latinos and African-Americans made up nearly one-third of the Democratic electorate in 2008 and are expected to account for more this time. A few recent surveys show a tight race, however.
Clinton's campaign has argued she would assert control of the Democratic race once it moved to more diverse states with black and Hispanic populations who have traditionally backed Clinton and have been slow to warm to Sanders.
But a Sanders win in Nevada would shatter that perception, fuelling new questions about Clinton's strength in a campaign that was once considered a cakewalk for her. It would also raise the stakes for the next contest, in South Carolina on February 27.
A Clinton win, however, would halt the momentum Sanders has generated from his 22-point defeat of Clinton in New Hampshire and position her to begin rolling up wins and delegates in South Carolina and on "Super Tuesday" on March 1.
On the Repubican side, front-runner Trump created some last-minute drama in South Carolina after Pope Francis said on Thursday his views on US immigration were "not Christian." Trump initially called Francis "disgraceful," but later called him "a wonderful guy."
The Vatican later clarified the pope's remarks, saying they were "in no way" a personal attack and were not an indication how to vote.
Trump also called for a boycott of Apple products until the tech company agreed to help the US government unlock the mobile phone of one of the killers in last year's San Bernadino, California, shooting.