WASHINGTON, April 29 (Xinhua) -- It seems that health care, a key issue in the 2018 U.S. midterm elections, may remain one of the top challenges for President Donald Trump's 2020 re-election campaign.

American voters, by a 17-point margin, say his handling of the issue makes them more likely to oppose than support him for a second term, according to the ABC News-Washington Post poll released Monday.

Overall, the poll found that 55 percent of respondents said they will not vote for Trump next year, with only 39 percent approving of his work since taking office.

The president has averaged just a 38 percent approval rating since he took office, the lowest by far for any president in his first two and 1/4 years in office in surveys dating back to Harry Truman's administration more than 70 years ago, said an ABC report.

Of the polled, 40 percent say Trump's handling of health care makes them more likely to oppose him for re-election, while 23 percent say it makes them more likely to support him.

Voters in the 2018 midterms selected health care as the top issue in their vote by a wide margin over three others offered, and those who picked it favored Democrats for Congress by a margin of 75 percent to 23 percent.

Meanwhile, 44 percent of the surveyed say they're more likely to oppose Trump for a second term based on his handling of immigration policy, versus 31 percent more likely to support him, a 13-point net negative.

The Mueller report produces a 22-point net negative score for Trump: 36 percent say it makes them more likely to oppose him for re-election, versus just 14 percent more likely to support him, the poll showed.

Trump's score on handling international trade is closer -- Americans by a net of 5 percentage points say it makes them more likely to oppose him for re-election. He also has a net 7-percentage point positive score on handling the economy, which will likely be the cornerstone of his re-election campaign.

Of those respondents who said they wouldn't vote for Trump, only 29 percent said they would for sure vote for his eventual Democratic counterpart. Nearly two-thirds instead said they would wait to see who emerges from the crowded Democratic field, which is currently made up of 21 candidates vying for the nomination.

As many as 85 percent of registered voters said they plan to vote in 2020, a high mark this far out from the presidential election, the poll found.

The survey interviewed 1,000 adults nationwide via phone from April 22 to 25 in both English and Spanish, with a margin of error of plus or minus 3.5 percentage points.