South Carolina’s Republican primary on Saturday looms as a crucial test in the 2016 presidential campaign, and it’s possible the Republican field will be further winnowed [thinned or reduced in size] after the results are known Saturday night.

Donald Trump leads all recent polls from South Carolina, with Texas Senator Ted Cruz and Florida Senator Marco Rubio vying for second place.  Farther back are former Florida governor Jeb Bush, Ohio Governor John Kasich and retired neurosurgeon Ben Carson. Trump said at a recent rally that a win in South Carolina could help him “run the table” in [win all] the rest of the primary and caucus contests to come.

A record of picking nominees

The South Carolina Republican primary has been a key indicator of the Republican Party's eventual presidential candidate. Since 1980 the primary winner has been the party's final choice to run in the general election every four years, except in 2012, when Newt Gingrich defeated Mitt Romney, who went on to win the nomination to challenge President Barack Obama.

South Carolina is the first of several states holding primary elections where southern conservatives and evangelical voters will hold sway [predominate]. This was thought to be a natural constituency for Ted Cruz, and it helped him win the Iowa caucuses earlier this month.

Trump has been surprisingly appealing to these voters, however. That portends well for him not only in South Carolina but in upcoming contests in several southern states including some of the so-called "Super Tuesday" contests in Alabama, Georgia and Louisiana.  

“We are going to win,” Trump told supporters at a recent rally. “We are not going to take this stuff anymore. We are going to do it right and we are going to make America great again.”

Fourteen states hold Republican primaries or caucuses on March 1, the busiest day in this year's political calendar.

Trump vs Bush

The Republican race in South Carolina has become increasingly bitter since last week’s contentious debate, which was marked by several clashes between Trump and Bush, among others.

Trump went after Bush over President George W. Bush’s decision to invade Iraq in 2003.

“They lied," Trump said of senior Bush administration officials. "They said there were weapons of mass destruction [held by Iraq's Saddam Hussein]. There were none, and they knew there were none!”

Former Florida Gov. Jeb Bush speaks during a Faith
Former Florida Gov. Jeb Bush speaks during a Faith and Family Presidential Forum at Bob Jones University in Greenville, S.C., Feb. 12, 2016.

Jeb Bush fired back that Republican voters were looking for: “Someone who doesn’t disparage people. Someone who doesn’t brag, for example, that he’s been bankrupt four times, and it was great because he could use the legal system.”

Bush added, “I am sick and tired of him going after my family. My dad [President George H.W. Bush] is the greatest man alive, in my mind.”

Bush has recruited his brother and his mother to help him win votes in South Carolina.  Former President George W. Bush did not mention Trump’s name but seemed to have him in mind during a campaign rally for Jeb in Charleston.

“I understand that Americans are angry and frustrated.  But we do not need someone in the Oval Office who mirrors and inflames our anger and frustration,” he said.

Campaign takes a nasty turn

Trump has also accused Ted Cruz of lying about his record and threatened to sue him over a Cruz ad that screens video from the 1990s showing Trump declaring his support for abortion rights.

“He is a lying guy, a really lying guy,” Trump said of Cruz in an appearance this week. “Some people misrepresent.  This guy is just a plain-out liar.”

Without discussing his statements of more than a decade ago, Trump now says he has long been "pro-life" - meaning, in American political parlance, that he opposes those who are "pro-choice," who support women's rights to freely choose abortion without government restrictions.

Republican presidential candidate Sen. Ted Cruz, R
Republican presidential candidate Sen. Ted Cruz, R-Texas, addresses the audience during a presidential forum at First Baptist North Spartanburg in Spartanburg, South Carolina, Feb. 17, 2016.

Cruz challenged Trump to go ahead with the lawsuit and said Trump’s past statements, as well as those of Marco Rubio, are fair game in the primary debate.  “And their strategy of screaming 'liar' whenever anyone points to their record and relying on fabrications is not indicative of candidates running honest campaigns,” Cruz said at a news conference.

Campaign's crucial phase ahead  

The battle between Cruz and Rubio for second place behind Trump in South Carolina is intensifying. Rubio may have gotten a late boost with endorsement of South Carolina’s popular governor, Nikki Haley.

“If we elect Marco Rubio, every day will be a great day for America,” Haley said at a joint rally in Chapin.

FILE - Gov. Nikki Haley, R-South Carolina, campaig
Gov. Nikki Haley, R-South Carolina, right, campaigns with Republican presidential candidate Sen. Marco Rubio, R-Florida, in Greenville, South Carolina, Feb. 18, 2016.

A poor finish by Jeb Bush in South Carolina could lead to calls for him to abandon his campaign.

The Republican race is about to enter a crucial phase.  Between Saturday’s primary in South Carolina and March 15, when key states including Florida and Ohio hold primaries, 36 states and territories will have held contests on the Republican side, choosing close to 60 percent of the total delegates to attend the national nominating convention in July in Cleveland.

The next month will tell us a lot about the Republican race but there are some Republican analysts who caution that a deadlocked convention is not out of the question.

Nevada Caucus for Democrats

The Democratic race shifts to Nevada Saturday for caucus voting - where Hillary Clinton is getting a strong challenge from Bernie Sanders.

“Leadership is not only leading the band when it is popular," he said. "Leadership is about standing up for what is right even when it is not popular.”

FILE - Democratic presidential candidate Hillary C
FILE - Democratic presidential candidate Hillary Clinton speaks in New York, Feb. 16, 2016.

Clinton is also focused on appealing to African-American voters in South Carolina, where Democrats vote on February 27.

“I want to tear down all the barriers that hold back Americans across racial lines because our country can only live up to its potential when every single American has a chance to live up to theirs,” she said.

One new national poll now shows Sanders and Clinton effectively tied among Democratic voters.