WASHINGTON — Hillary Clinton holds a double-digit, but narrowing, lead nationally over Sen. Bernie Sanders in the contest for the Democratic presidential nomination, according to a new Washington Post-ABC News poll.

Clinton’s

reduced lead nationally reflects heated competition in Iowa and New Hampshire. While she is still seen as the front-runner, victories by Sanders in the first two states on the primary-caucus calendar could quickly change perceptions nationally and probably would result in a more prolonged and costly battle for the nomination.

Over the past month, the former secretary of state’s national margin has shrunk by 12 percentage points. The current poll shows her leading Sanders by 55 percent to 36 percent among registered Democrats and Democratic-leaning independents. December’s poll had shown her the choice of 59 percent, to 28 percent for Sanders. Former Maryland governor Martin O’Malley runs far back, with just 4 percent.

Clinton owes her national lead to overwhelming support among nonwhite voters. Among white Democrats, she and Sanders are about even (45 percent to 43 percent). Among nonwhite voters, she leads by 67 percent to 28 percent, although Sanders has cut into that margin in the past month.

advertisement | advertise on newsday

Another fault line the poll highlights is Clinton’s strength among self-identified Democrats and Sanders’ support among independents. Clinton leads by 26 points among self-identified Democrats, while Sanders has a slender (49 percent to 43 percent) lead among independents who lean Democratic.

The other big demographic line of demarcation is the split between younger and older voters. Among voters under the age of 40, Sanders leads Clinton by 19 percentage points. Among those age 40 and older, Clinton leads by 36 points.

The Post-ABC poll was conducted Jan. 21-24 among a random national sample of 1,001 adults reached on landline and cellular phones. The margin of sampling error for overall results is plus or minus 3.5 percentage points; the error margin is 5.5 percentage points among the sample of 406 Democratic and Democratic-leaning independent registered voters.