Results of the Washington Post-ABC Poll released Wednesday showed Clinton has the backing of 73 percent of Democrats and Democratic-leaning voters, overwhelming Vice President Joe Biden, who had 12 percent in a 2016 primary bout.
Sen. Elizabeth Warren of Massachusetts was third with 8 percent.
The hypothetical race for the GOP presidential nomination was less clear, with six prospective candidates registering 10 percent to 20 percent support, the Post said. No candidate has broad backing from both Tea Party activists and mainstream Republicans.
New Jersey Gov. Chris Christie, who was at or near the top of the Republican field in many public opinion surveys last year, appears to have taken a political hit from the bridge traffic scandal tarnishing his administration.
The latest Post-ABC News survey had Rep. Paul Ryan of Wisconsin in the lead with 20 percent, followed by former Florida Gov. Jeb Bush at 18 percent and Christie with 13 percent. Sens. Ted Cruz of Texas, Rand Paul of Kentucky and Marco Rubio of Florida were at 12 percent, 11 percent and 10 percent, respectively.
None of the Democrats or Republicans has clearly stated an intent to mount a White House bid in 2016. Warren has said she won't run.
Results are based on a nationwide phone sample of 1,003 adults conducted Jan. 20-23. The margin of error is 3.5 percentage points.