Since taking office in 2002, Graham has never been in a runoff in the Republican primary, but undecided voters could break his streak.

Sen. Lindsey Graham (R-SC), who has faced primary challenges in nearly every Senate election, has never been forced into a runoff.

South Carolina voters are narrowing down candidates in key races for governor and U.S. Senate. Republicans in both contests have played up their ties to Donald Trump, who remains…