House Speaker Paul Ryan has won over an unlikely ally to salvage his controversial tax plan: Steve Bannon.

Trump's top strategist once described Ryan as "the enemy," but now the former Breitbart News chief is the speaker's best chance to win approval for his border-adjusted tax, which Republicans currently say has almost no hope of clearing the Senate.

In a handful of White House meetings, Ryan found that Bannon was perhaps the most enthusiastic backer of the border-adjustment plan, according to a senior administration official and a person familiar with the sessions.

A vigorous endorsement from Donald Trump could help save the border-adjustment plan, which is running into strong opposition from the energy industry and retailers.