Hillary Clinton. REUTERS/Jim Bourg Former Secretary of State Hillary Clinton held a narrow lead over Sen. Bernie Sanders (I-Vermont) in Iowa, according to a survey released Saturday by the most historically accurate pollster in Iowa.

The Bloomberg/Des Moines Register poll found Clinton leading Sanders, 45% to 42%, among likely Democratic caucus-goers.

Former Maryland Gov. Martin O'Malley (D) got 3%, in the survey, which was conducted by veteran pollster J. Ann Selzer.

Iowa Democratic polls have varied widely over the past two weeks. But in a RealClearPolitics average of seven recent surveys, Clinton now holds a narrow, 3.2-point advantage over Sanders heading into Monday's Iowa caucuses.

The Bloomberg/Des Moines Register poll found several encouraging signs for Clinton. First, only a third of likely voters in Iowa were first-time caucus-goers. Those voters overwhelmingly chose Sanders.

Second, Clinton's support appears stronger than Sanders'. Among Clinton supporters, 83% said their minds were made up. Only 69% said the same about Sanders, a percentage that has gone down from the last survey in December.

"Most of the ways you look at it, she’s stronger than the three-point race would suggest," Selzer said.

Sanders has been surging in both Iowa and New Hampshire, which holds the first traditional primary vote on February 9, over the past few weeks. He has also narrowed Clinton's once-overwhelming advantage nationally.

Selzer's poll is widely respected in the political world. In a profile this week, the statistical news website FiveThirtyEight called Selzer "the best pollster in politics." The Register noted that her poll is known as the "gold standard" due to its historical accuracy. A Politico profile last December further described her as "legendary."