WASHINGTON (CNN) Former Vice President Joe Biden holds the pole position in the first CNN/Des Moines Register/Mediacom poll among likely 2020 Democratic caucusgoers, with Vermont Sen. Bernie Sanders and Texas Rep. Beto O'Rourke joining him as the only possible candidates in the field with double-digit support.

The new Iowa Poll finds 32% of likely caucusgoers saying they back Biden as their first choice, 19% Sanders, 11% O'Rourke, 8% Massachusetts Sen. Elizabeth Warren, 5% California Sen. Kamala Harris, with the rest of the 20-person field testing below 5% support.

The top three candidates in Iowa, including O'Rourke's third-place ranking, match the top three in a national CNN poll released Friday . Early results nationally are often driven by name recognition, but in Iowa, the campaign is already underway, with several of the tested candidates having made multiple visits to the state, and at least one having already visited all 99 of the state's counties.

Iowa's caucusgoers, who get the first formal say in who the party's nominee will be, mostly say they are looking for a winner (54% want a candidate who can defeat Trump) over ideological purity (40% want one who shares their positions on major issues). Those who prioritize a winning candidate are more apt to back Biden and O'Rourke than the overall pool of likely caucusgoers (36% in that group say they favor Biden, 14% Sanders, 14% O'Rourke) while Sanders outperforms his overall number among those looking for a candidate who shares their issue positions (30% Biden, 26% Sanders, 8% O'Rourke).

Overall, more say that nominating a seasoned political hand (49%) would be a better way for the Democrats to try to to defeat Trump than to nominate a newcomer to politics (36%), and the bevy of senators (plus one congressman) atop the field may reflect that preference. The political newcomers tested -- businessmen Tom Steyer and Andrew Yang -- both failed to register much support in the poll.

Most of Iowa's likely Democratic caucusgoers say they'd prefer to see a field with a number of strong contenders (52%) rather than a race dominated by one strong candidate emerging early as a clear frontrunner (41%), and the poll's findings suggest they are open to considering a large number of candidates. That's a contrast with the mood of Democrats nationwide, a majority of whom, after a bruising 2016 nomination battle that lasted through the entire primary season, say they are hopeful for the quick ascension of a frontrunner, according to CNN's poll.

Beyond the horse race question, the Iowa survey asked likely caucusgoers if they could ever consider each of the candidates tested in the poll who they did not choose as their first- or second-choice candidate, or if they would never support that person. Nearly half (46%) of likely caucusgoers said there wasn't a single candidate in the field they would never support. Another 12% said there was only one candidate they would rule out.

And many of those tested in the survey remain unknown, even to Iowa's politically active caucusgoers. Majorities said they could not offer an opinion on 12 of the 20 potential candidates when asked a basic favorability rating.

Of the better-known candidates in the field, four merited favorable views from a majority of likely caucusgoers -- Biden (82% favorable), Sanders (74%), Warren (64%) and O'Rourke (53%). Booker and Harris weren't far behind with 49% rating each of them favorably, and former Attorney General Eric Holder also topped 40% favorability, landing at 42% in the poll.

Although Holder doesn't register much support as a first or a second choice -- just 1% say they would put him in their top two right now -- 50% say they would ever consider backing him for president, a higher number than just about anyone else who ranked that far down the first-choice scale. New York Sen. Kirsten Gillibrand also comes close with 48% saying they'd consider her, though her favorability rating is a bit lower at 35%.

What Iowa Democrats seem certain about is that they don't want to see another run from Hillary Clinton. Almost three-quarters say that if she were to get in the race she would detract from it (72% say so), and her favorability rating is narrowly upside down, with 49% holding an unfavorable opinion vs. 47% who have a positive view.

Two others who have flirted with presidential runs are also seen as more apt to detract from the race than to add to it: Oprah Winfrey (55% say she would do more to detract than add) and Howard Schultz (55% detract). Views on Michelle Obama, however, tilt sharply in the opposite direction. Three-quarters say she would add to the race for president should she throw her hat in the ring (76%), while just 22% say she would detract from it.