Senator Bernie Sanders speaks during a Democratic Town Hall event in Des Moines, Iowa. (Patrick T. Fallon/Bloomberg)

Hillary Clinton speaks during a Democratic Town Hall event in Des Moines, Iowa. (Patrick T. Fallon/Bloomberg)

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 is seen as more electable and stronger on most issues but has a deficit against her rival on the question of honesty and trust.

Clinton’s reduced lead nationally reflects heated competition underway in Iowa and New Hampshire, the first two states on the primary-caucus calendar. While Clinton is still seen as the front-runner in the Democratic race, victories by Sanders in Iowa and New Hampshire 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. That compares with December’s poll, which showed her the choice of 59 percent to 28 percent for Sanders. Former Maryland governor Martin O’Malley runs far back in third place 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.

That disparity between white and non­white support illustrates the challenge for Sanders once the campaign moves from two largely white states to South Carolina, Nevada and elsewhere, where African Americans and Hispanics play a more significant role.

Another fault line the poll highlights is Clinton’s strength among self-identified Democrats and Sanders’s 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 poll finds only modest differences in support along ideological lines, despite each candidate’s significantly different proposals for government’s role in the economy and health care. Clinton leads by 25 percentage points over Sanders among moderate and conservative Democrats, and by 10 points among liberals.

The poll also underscores the degree to which Clinton’s recent efforts to tie herself more closely to President Obama can help her. The poll shows that 83 percent of Democrats and Democratic-leaning independents approve of Obama’s job performance, with 57 percent approving strongly. Among those who strongly approve of the job Obama is doing as president, she leads Sanders by about 2 to 1. Among those who disapprove or say they only “somewhat” approve of his performance, she and Sanders are even.

Clinton has made electability part of her closing argument before Iowa, and the poll shows that nearly 2 in 3 Democrats see her as more electable than Sanders in a general election. She also holds a wide lead (58 percent to 30 percent) on the question of which candidate has the temperament and personality to serve as president.

Clinton and Sanders are more evenly matched on two other attributes. Although the Vermont senator is running as the politician who would shake up the status quo, slightly more Democrats (49 percent to 42 percent) say Clinton would bring needed change to Washington. On the question of which candidate is “closer to you on issues,” the results are Clinton 47 percent and Sanders 43 percent.

Sanders, however, has widened his advantage on the issue of who is more honest and trustworthy. In October, the two were at parity on this question. That became a six-point advantage for Sanders in December. Today, it is a 12-point advantage, with 48 percent saying he is more honest and trustworthy to 36 percent for Clinton.

Democrats see Clinton as far better prepared to handle most of the major issues. She enjoys leads ranging from 18 points to 41 points on the economy, immigration, health care, the threat of terrorism and dealing with an international crisis.

Sanders’s lone advantage is on the issue of regulating banks and other financial institutions, where he is favored by 48 percent of Democrats to 42 percent for Clinton. Sanders has called for breaking up the biggest banks and has complained that no executives from financial institutions went to jail after the 2008 economic collapse.

Yet Sanders, a self-identified democratic socialist who favors transformative expansion in government’s role in health care and the economy, has so far avoided the perception that he is too liberal to win a general election.

More than two-thirds of Democrats in the survey expect Sanders would defeat potential Republican nominees Sen Marco Rubio (Fla.), Sen. Ted Cruz (Tex.) and businessman Donald Trump in a general election. Still larger majorities are confident in Clinton’s ability to win against each of these candidates.

The Post-ABC poll was conducted Jan. 21-24 among a random national sample of 1,001 adults reached on land-line 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.