Although Rubio doesn’t show up in the upper tier, he tops the list of contenders whom likely caucusgoers say is their second choice. Beyond that, 49 percent say they’re willing to consider him. Rubio, who would become the nation’s first Latino president if he wins the White House, also ranks third highest in favorability — 60 percent view him positively, and just 17 percent unfavorably.

“It really does suggest he’s poised to break,” pollster J. Ann Selzer said.

The underlying numbers show Bush, a relative of two previous U.S. presidents, has a tougher path in Iowa than Rubio. Bush is viewed unfavorably by more likely caucusgoers (45 percent) than anyone else except for Donald Trump, a Manhattan businessman turned reality TV personality (63 percent) and New Jersey Gov. Chris Christie (58 percent), who is known for his occasionally bellicose East Coast behavior.

And asked if they could ever support Bush for president, a third said no, never.