Former Vice President Joe Biden's lead over his closest rival in the 2020 Democratic primary field continues to narrow in South Carolina, according to the latest Post and Courier-Change Research poll.

The survey, which was released on Sunday, shows that Biden now holds just a 5-point lead over Sen. Bernie Sanders (I-Vt.) in the Palmetto State. Biden, who once led by more than 30 points in South Carolina, earned support from 24 percent of likely Democratic primary voters, a 3-point decrease from a similar survey in December.

Meanwhile, 19 percent of likely Democratic primary voters said they favored Sanders as the Democratic presidential nominee. Seventeen percent of respondents put their support behind billionaire philanthropist Tom Steyer, representing a 12-point jump since December.

Sen. Elizabeth Warren (D-Mass.) was the only other candidate garnering double-digit support, with 10 percent of respondents endorsing her nomination. Former South Bend, Ind., mayor Pete Buttigieg came in fifth with 6 percent support.

The findings come just a day before voting kicks off at the Iowa caucuses, the first-in-the-nation vote of 2020. Over the last couple months, Sanders and Biden have emerged as the frontrunners among the field, with Biden leading most national surveys and Sanders ahead in Iowa and New Hampshire, the second state to hold a primary vote.

According to a Real Clear Politics average of surveys, Sanders holds a 3.6-point lead over Biden heading into the Iowa caucuses on Monday.

While Biden's lead has narrowed since he earned 46 percent support last May, no other 2020 Democratic contender has polled at more than 20 percent in a Post and Courier-Change Research survey.

Biden also continues to hold a substantial lead over his opponents among African Americans, who make up a majority of the Democratic electorate in South Carolina. Thirty percent of black respondents favor Biden, while 24 percent support Steyer. Sanders trailed them both with 16 percent support from black respondents. Warren earned 10 percent support.

Buttigieg, who continues to struggle to make inroads with African Americans, polled at 2 percent among black voters.

Polls indicate that Iowa, New Hampshire and Nevada - the first three states to hold primaries - could feature tight races between Biden, Sanders, Warren and Buttigieg. But surveys have mostly shown Biden to hold a solid advantage in South Carolina. A Fox News survey of the state released in January found that Biden led the field by more than 20 points.

The Post and Courier-Change Research survey was conducted among a sample of 651 likely Democratic primary voters between Jan. 26 and Jan. 29. It has a margin of error of 4 percent.