WASHINGTON—Barack Obama has won over more than half of Hillary Rodham Clinton’s former supporters, according to an Associated Press-Yahoo News poll that finds party loyalty trumping hard feelings less than three weeks after their bruising Democratic presidential contest ended.

The poll suggests time is beginning to heal some rifts from the primary campaign and that the New York senator’s endorsement of Obama carried weight. The poll was taken in the days after Clinton suspended her campaign and said she was supporting her rival.

Obama’s progress with Clinton supporters is marked, yet far from complete. More than one in five who had backed the New York senator now plan to support Republican John McCain in the fall, a boost for McCain if those opinions hold.

“We still have work to do,” Obama campaign manager David Plouffe told reporters in a strategy briefing. “Democrats are consolidating behind the nominee as the choice in the election is more clear and as the contest fades. Time is our friend here.”

Obama’s outreach to Clinton supporters picks up this week. Clinton planned to introduce Obama to her financial backers Thursday night in Washington, and the two will campaign together for the first time Friday in New Hampshire.

“I want her campaigning as much as she can,” Obama told reporters Wednesday. “She was a terrific campaigner. She, I think, inspired millions of people, and so she can be an extraordinarily effective surrogate for me and the values and ideals we share as Democrats.”

The AP-Yahoo News poll, conducted by Knowledge Networks, is part of an ongoing study that tracks the attitudes and opinions of a scientifically selected group of more than 2,000 Americans to see how their political views evolve over the course of the campaign.