WASHINGTON — A trio of Republican establishment favorites — Jeb Bush, Scott Walker and Marco Rubio — are all losing ground in the party’s 2016 presidential field, a new Fox News poll shows.

Donald Trump, meanwhile, continues to dominate the race — earning 25% support nationally while another outsider, retired neurosurgeon Ben Carson, is running second at 12%, and Texas Sen. Ted Cruz, known for locking horns with Republican congressional leaders, is third at 10%.

Bush, the former Florida governor, has dropped to 9% — fourth place, down from 15% and second place in a Fox News poll conducted earlier this month, before the first GOP presidential debate.

Walker, the Wisconsin governor, meanwhile, is tied for fifth, at 6% — down from 9% earlier this month. And Rubio, the Florida senator, is now at 4% — in ninth place, and down from 5%.

The results — with outsiders at the front of the field and establishment favorites struggling to gain traction — reflect a shift among likely Republican primary voters toward candidates who challenge the political hierarchy.

In the new Fox News poll, former Arkansas Gov. Mike Huckabee tied with Walker for fifth at 6%. They’re followed by former Hewlett Packard CEO Carly Fiorina at 5%, Ohio Gov. John Kasich at 4%, Rubio, and then New Jersey Gov. Chris Christie and Kentucky Sen. Rand Paul, who both at 3% support.

The poll was conducted Aug. 11-13. It has a margin of error of plus or minus four percentage points.