Bernie Sanders has claimed that if he were to become the Democratic Party’s presidential nominee it would be a windfall for his party in down-ballot elections, saying he would energize young people and other base voters who don’t regularly show up. But some operatives tasked with electing Democrats in red and purple states aren’t just concerned a Sanders nomination would make an already difficult job impossible – they fear a “nightmare” scenario.

Democrats outside the party’s core areas have had a rough eight years under President Obama, losing control not only of both chambers of Congress, but many gubernatorial mansions and state legislatures as well. The party is counting on 2016, a presidential year when high-turnout favors Democrats, to at least win back the Senate and to begin making gains elsewhere.

“You’ve heard Bernie make the point that Democrats win when there are big turnouts. Republicans win when people are discouraged and don’t vote,” said spokesperson Michael Briggs. “He’s the candidate with the enthusiasm and energy that will help Democrats up and down the ticket win in November.”

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But several campaign managers and other senior operatives currently working on down-ballot campaigns, all whom spoke only on condition of anonymity, said that while they don’t doubt Sanders can drive turnout in liberal areas, he would make life difficult outside blue states. Instead, they favored front-runner Hillary Clinton, who they said can appeal to more moderate voters and especially those concerned about national security.

“I don’t know how you run a campaign in a southern or red state with a democratic socialist at the top of the ticket,” said the campaign manager for one red state Democrat. “It becomes near impossible to separate yourself enough to win over the conservative independents you need to win.”

It’s a similar warning to the one raised this week by Clinton allies Missouri Gov. Jay Nixon and Rep. Steve Cohen – and people on the ground and in the trenches working to elect Democrats have an even more tactical view.

“I think it would be a nightmare, plain and simple,” said one former Blue Dog staffer current working on a statewide campaign in a state Obama did not win. “It’s something that’s starting to come up in conversation with decent regularly. People are concerned about what affect it would have on the entire rest of the ballot from state legislators to gubernatorial and Senate races.”

Not everyone agreed. Bill Phillips, who is hoping to unseat Rep. John Mica in a Florida swing district, said it’s too early to tell. The energy around Sanders’ campaign might lead to unusual high turnout and Democratic victories. Still, he said Clinton is probably a safer bet. “What’s more clear is Senator Clinton,” he said, “does better with key Democratic constituencies.”

In red states and districts, down-ballot candidates need to do better than the person at the top of their ticket. There may simply not be enough Democratic base voters to win an election in many of these districts, no matter how much Sanders energizes people. That means they need to convince voters to support them, even if the same voter is backing a presidential candidate of a different party.

“It’s hell of an anchor around the neck of any down-ballot candidate,” said a Democratic strategist involved in several House races in non-blue states. “For Democratic candidates in places where the competitive house seats are, mid-wester states, in western states, in swing districts, in suburban districts, in places where you have to outperform your presidential candidate, I think it would be incredibly hard.”

The strategist doubted whether Sanders even could drive higher turnout, considering he has struggled to energize minority voters and lacks the historical imperative of both of Obama’s presidential bids or Clinton’s.

Jim Manley, a Senate Democratic strategist who has worked for some of the chamber’s more liberal members, worried Sanders-mania would not translate to other candidates. “His supporters may like him – but I doubt they are going to lift a finger to help anyone else down ballot,” he said.

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Republican operatives have been on high alert since Republican front-runner Donald Trump moved to the top of polls, trading memos and public opinion data on what impact he would have down-ballot and how the party’s candidates can best mitigate his impact.

Democrats in Washington seem to be biding their time. “We’re not drawing up any contingency plans or freaking out,” said one Democratic strategist with working knowledge of House races.

But Sanders’ surge in Iowa has prompted phone calls and emails to fly across state lines in the South, Midwest, and West as strategists try to figure out how to respond in case their candidate is asked about Sanders. Some have discussed the need to be pro-active in distancing their candidate from Sanders, even floating the idea of a press conference all-but-disowning Sanders if he were to become the nominee.

A senior Senate campaign staffer in a swing state compared Sanders’ impact to that of Trump on the Republican side.

“You’re seeing it with the Trump issue every day. Every day, a Republican in some senate or some house race is having to issue a state saying I don’t agree, I do agree, or doing some convoluted dance under their party’s front-runner,” the operative said. “That creates kind of day-to-day challenges for a campaign. It distracts you from getting your message out, and it’s not helpful in convincing independent voters.”

And in differentiating themselves from Sanders, candidates would face the challenge of calibrating their response just right, so as not to turn off base voters. It could be a lose-lose situation either direction they move.

But Phillips, who is running for Congress in Florida, says Trump or Sen. Ted Cruz at the top of the Republican ticket could just as much impact the Democratic race as who is on the Democratic ticket. “Before we know both nominees, it’s difficult to say with real authority that Sen. Sanders would be good or bad,” Phillips said, adding that election are “often about contrasts.”

Sanders’ campaign disputes the premise raised by the strategists, saying their candidate has proven he can win independents, a group among whom he outperforms compared to registered Democrats in Iowa and New Hampshire.

“Are these the people who helped their candidates secure the current majorities that Democrats hold in the Senate and the House and statehouses across the country? Just curious,” Briggs quipped.