A new poll shows Hillary ClintonHillary Rodham ClintonOvernight Cybersecurity: Anticipation builds for Trump cyber order | House panel refers Clinton IT contractor for prosecution | Pentagon warned Flynn about foreign payments Trump’s foreign policy of more is about money Meghan McCain: Obama 'a dirty capitalist like the rest of us' MORE and Bernie SandersBernie SandersOvernight Energy: Trump set to sign offshore drilling order Meghan McCain: Obama 'a dirty capitalist like the rest of us' Dems might begin again with Kamala Harris and California MORE running neck and neck among likely Democratic caucusgoers in Iowa.
The Vermont senator widened his lead over the former secretary of State to 19 points in New Hampshire, however, a 15-point jump from a similar poll earlier this month. New Hampshire will vote on Feb. 9.
Clinton remains dominant in South Carolina, with a 37-point lead over the Vermont senator, 64 percent to 27 percent.
Former Maryland Gov. Martin O'Malley holds the third spot in all three states, pollsters also found, with 3 percent in Iowa, 2 percent in New Hampshire and 2 percent in South Carolina.
Clinton and Sanders's tight race in Iowa — which holds its caucuses on Feb. 1 — could give the victor a decisive early advantage in the Democratic race for president.
"If Clinton carries Iowa, she can absorb a defeat to Sanders, who has a home field advantage in New Hampshire, and then move on to South Carolina," said Lee Miringoff, director of the Marist College Institute for Public Opinion. "If Sanders carries Iowa and then New Hampshire, this contest will, indeed, be a marathon."
Thursday's poll additionally found that 7 percent of likely voters are undecided in South Carolina, which will hold the fourth Democratic contest, on Feb. 27.
Mark Hensch contributed to this report.
Updated at 7:33 a.m.