Earlier today, Paul Waldman asked a good question: Why can’t vulnerable Senate Democrats call for public calm about Ebola, rather than endorsing a travel ban to defuse GOP fear-mongering tactics? Would such a measured response really have to mean instant political self Ebolization?

As far as I can gather there are two reasons Democrats are caving. The first: Democrats think the GOP strategy of layering Ebola on top of ISIS and the child migrant crisis is successfully spreading generalized public anxiety in a way that is having a palpable impact on the elections. As I’ve said before, the GOP strategy is about creating political atmospherics that nationalize Senate races, changing the subject away from issues and GOP candidate vulnerabilities that play in favor of Democrats, and filling voters with a sense that everything is whirling out of control on Democrats’ watch. The specifics of the debate — which strongly suggest a travel ban could be counter-productive or even disastrous, as Jonathan Cohn has comprehensively explained — are largely beside the point.

It doesn’t help that there appears to be no level of GOP fear-mongering about Ebola that that will attract anywhere near the level of media disapproval that has been directed at Alison Lundergan Grimes’ “disqualifying” refusal to say whether she voted for Obama, as Brian Beutler details today.

The second reason Dems in tough races are coming out for a travel ban is that it helps resolve a strategic dilemma some advisers say these candidates face: How to achieve the requisite distance from Obama without depressing efforts to get out core voters.

This problem is kicking in at this particular moment because, with early voting underway, Democrats are seeking to counter their “midterm dropoff problem” by bringing in as many people who didn’t vote in 2010 as possible. At the same time, though, Democrats are trailing by small margins in tough races largely because whatever persuadable voters remain come from constituencies who really dislike the president. In Colorado we’re talking about independent men and to a lesser extent suburban women. In Arkansas it’s married white women. The challenge for Democrats is to signal independence from Obama, who is unquestionably weighing them down among these voters, without alienating what one strategist calls the “2012 surge voters” that Democrats need to do a better job of bringing in during this midterm election.

As Sheryl Gay Stolberg explains in a good piece, African American voters who did not vote in 2010 could play a pivotal role for Democrats in places like Arkansas, Louisiana, Georgia, and North Carolina. Yet the president is deeply unpopular in these places, so his get-out-the-vote appeals are limited to targeted ones.

Meanwhile, Democratic efforts to create distance from Obama risk creating problems in reaching these voters, strategists confide. In Kentucky Alison Lundergan Grimes has aggressively distanced herself from the president on energy and coal, but this risks alienating environmental progressives in places where she’ll need a huge turnout, such as Louisville.

“They don’t like the fact that Alison continues to emphasize her disagreement with Obama on coal,” Dem Rep. John Yarmuth tells me, adding that he is stepping in where possible to rally environmental progressives in his Louisville district to get behind Grimes anyway: “I say, `What do you think is worse for climate change — junior Senator Alison Grimes or a Republican majority led by Mitch McConnell’?”

As the First Read crew puts it today: “if the Democratic Party wants to energize its voters, is treating the head of the party like a pariah the best way to do that?” First Read added: “running away alienates many of the voters who elected — and then re-elected — him.”

But calling for a travel ban creates distance from the president while allowing Democrats to remain Democrats while talking to the base — something that is complicated by, say, hitting Obama on coal or keeping the Affordable Care Act at arm’s length. As another Dem strategist put it to me, urging a more aggressive response to Ebola allows Dems to demonstrate “independence from Obama on matters of implementation and execution while still motivating the base on core policy distinctions.”

This sort of calculation isn’t pretty. But neither is the GOP fear-mongering strategy that has led many Democrats to the point of thinking such a calculated response is necessary.