But "because of independents and undecideds, this thing is still very fluid. A lot has to do with turnout,” says Brown Prof. James A. Morone

Hillary Clinton leads Bernie Sanders 43 percent to 34 percent heading into Tuesday’s Democratic presidential primary, and Donald Trump leads the Republican field with 38 percent, trailed by John Kasich with 25 percent and Ted Cruz with 14 percent, a new Brown University poll shows.

“Both Trump and Clinton are in the lead, and both are solid within their parties,” Brown Prof. James A. Morone said Sunday. “But because of independents and undecideds, this thing is still very fluid. A lot has to do with turnout.”

Usually, the smallest state has a small impact on presidential politics. But Clinton and Kasich campaigned here Saturday, Sanders spoke here Sunday and Trump arrives here Monday as candidates continue scrambling for delegates. “The front-runners are leading but they have not put it away,” Morone said. “So everybody is coming here.”

And people here are still making up their minds. “One striking feature of both primary races is that a large number of undecided voters are among those likely to vote: 17 percent of Republicans and 16 percent of Democrats were still not sure which candidate they will vote for on Tuesday," Brown's Taubman Center said.

In “closed” primaries, you can only vote in your party’s primary. But Rhode Island has a “semi-closed” primary system that lets independents vote in either party's primary, and 50 percent of the state’s voters are independents.

Among independent voters who plan to vote in the Democratic primary, 42 percent favor Sanders, 22 percent favor Clinton and 24 percent remain undecided. “Clinton wins with Democrats by a solid 2-to-1 ratio, so if this is a closed primary, it’s Hillary all the way,” Morone said. But if the undecideds and independents break heavily for Sanders, "it's going to be a late night," he said.

Likewise, Trump gets 49 percent of the Republican vote, so "if it’s a closed primary, he walks away with it,” Morone said. But among independents, Trump and Kasich each get 31 percent, Cruz gets 13 percent and 18 percent are undecided. And in other states, late-breaking undecided voters have tended to oppose Trump, "so if the undecideds break heavily against Trump, Kasich could conceivably squeeze this out," he said. "But we expect a strong second for Kasich.”

Asked about the poll Sunday, Sanders said, "I think we have a good shot to win here in Rhode Island. As the longest serving independent in the history of the U.S. Congress, I think we do well in virtually all of the contests with independents. I think independents can and will play a very important role here in the Rhode Island primary.”

State Clinton chairman Joseph M. McNamara said, "We are not taking anything for granted. It’s not about how many people you get to the park, it’s about how many people you get to the polls." State Trump chairman Joseph A. Trillo said, "I’m very happy that he is up. I’d like to see him up even more." State Kasich co-chairman Gary S. Sasse said, "Kasich is poised to pull an upset. Strong get-out-the-vote can make the difference." State Cruz co-chairman Giovanni D. Cicione said, "Trump has plateaued and we have strength among younger, more motivated voters."

The poll of 600 likely primary voters on April 19-21 has an overall margin of error of 4 percent. The GOP sample of 164 voters has a 7 percent margin of error.

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