Donald Trump just passed a historic test toward winning the GOP nomination

The prospect of Donald Trump winning the Republican nomination for president is starting to look more and more likely after what was shaping up to be a decisive win Saturday night.

The real-estate mogul was projected to win the South Carolina Republican primary. Combined with a win earlier this month in New Hampshire, it's a good indication of his chances at securing his party's nomination.

Trump is one of four GOP candidates to have won both the New Hampshire and South Carolina primaries since 1980.

The other three - Ronald Reagan in 1980, George H.W. Bush in 1988 and 1992, and John McCain in 2008 - went on to win the nomination.

And since the South Carolina primary's inception in 1980, every Republican winner has gone on to win the nomination - with one exception.

In 2012, former House Speaker Newt Gingrich won the South Carolina primary but ultimately lost the nomination to former Massachusetts Gov. Mitt Romney. The Gingrich campaign's momentum in the South eventually faded, and he lost primaries in Alabama and Mississippi.

But Trump is expected to do well in the South - he's leading polls in Georgia, and southern states have been a big part of his campaign's strategy.

Trump still has a long road ahead of him, however. Ted Cruz, the Texas senator, is likely to prove a strong competitor to Trump in the South. The conservative stalwart boasts strong support among evangelical voters, of which there are many in southern states.

Republican candidates are now heading into the fourth early-state contest in Nevada. The Republican caucuses there will take place on Tuesday. Trump is ahead there by an average of 22 points in recent polls, with Cruz placing second.

Trump's South Carolina win came after a narrow loss to Cruz in Iowa and a blowout win in New Hampshire.