If Bernie Sanders wins Iowa Monday and gains momentum, that would spook the stock market

New Hampshire's primary is the following week, and Sanders won there in 2016."I think the market really has run up for a lot of reasons, but they clearly have been pricing in a Trump re-election," said Lori Calvasina, chief U.S.equity strategist at RBC. Sanders is also leading Biden by a wider average 9.5 percentage points in polls in his neighboring state of New Hampshire."Anybody who has won two of the first three, they've all gone on" to be the nominee, said Daniel Clifton, head of policy research at Strategas.Read more: Voters largely favor capitalism over socialism amid Sanders' riseBiden is leading in the third and fourth states scheduled to hold votes. The early states, which are often disregarded as not important, create momentum for winners and really start to hurt the losers," Clifton said.This year, there is an early "Super Tuesday" of primaries on March 3 in more than a dozen states, including Texas, North Carolina and California, a key state where Sanders now has a large lead. "What looks like is happening is the progressive vote is coalescing around Sanders and feeling like he's got at least as good a chance as anybody else," said Laperriere, who heads U.S. policy at Cornerstone.Laperriere said an analysis on FiveThirtyEight Politics shows a win in Iowa could give a big boost to either candidate but would push Biden closer to being the nominee. Biden is less of a risk for the market, but the odds of him beating Trump are higher."Tom Block, Washington analyst at Fundstrat, said Iowa could determine which of party's progressive candidates will be left standing."It appears Sanders is gaining momentum, and Elizabeth Warren is losing momentum.