DES MOINES, Iowa - Donald Trump has elbowed his way back into the lead of the Republican race for president in Iowa, where the first votes for the 2016 nomination are about to be cast, according to a new Des Moines Register/Bloomberg Politics poll released Saturday evening.

Trump stands at 28 percent in the Iowa Poll among those likely to caucus Monday, with Texas Sen. Ted Cruz at 23 percent, down two points from earlier this month. Florida Sen. Marco Rubio, who has been surging in the state, clocks in at 15 percent. Retired neurosurgeon Ben Carson is running fourth at 10 percent.

Kentucky Sen. Rand Paul polls at 5 percent, and none of the rest of the candidates, including the establishment-friendly governors, has more than the 3 percent who support Gov. Christie.

"That's what they want, disruption of this system," Iowa-based pollster J. Ann Selzer said in a briefing for reporters on the Bloomberg Politics television set in downtown Des Moines. She added that there was some fluidity among the second-tier candidates but noted their combined support was lower than Cruz's.

On the Democratic side, Hillary Clinton is the top choice of likely caucus-goers, with 45 percent, to 42 percent for Vermont Sen. Bernie Sanders, the self-described democratic socialist. Former Maryland Gov. Martin O'Malley has 3 percent, the poll finds.

Eighty percent of the Democrats say it is time for a female president, vs. 11 percent who say it isn't. Asked whether it would be OK to have a socialist as the party's nominee, 68 percent say yes, and 25 percent disagree.

"That never came up 10 years ago," Selzer said. "I couldn't imagine ever asking the question."

Age is the big divide among Democrats. For instance, Sanders is leading among women under 45 years old, 48 percent to 33 percent. Yet 55 percent of women older than 45 back Clinton.

The Iowa poll was conducted Tuesday through Friday based on telephone interviews with 602 registered voters who say they definitely or probably will attend the Republican caucuses, and 602 registered voters who say they will definitely or probably attend the Democratic caucuses.

Results for each sample are subject to a margin of error of plus or minus 4 percentage points.