Stanley Greenberg, one of the top Democratic pollsters, warned that there is a “very real risk” that young voters will not turn out for Democrats in the 2018 midterm elections.

Greenberg’s remarks to the Atlantic’s Ron Brownstein this week underscores how the left is getting more worried that the so-called “blue wave” they once took for granted may not materialize in November.

As Brownstein noted, Greenberg’s remarks would not have worried Democrats six months ago when Democrats “held an advantage across the age spectrum when voters were asked which party they preferred in the midterm elections.” But recent polling has shown that the left’s advantage had significantly dissipated.

A recent CNN midterm poll, for instance, found that Democrats only have a three-point advantage over Republicans, as the percentage of Americans who think things are going “well” in America is at its highest since 2007.

A recent Reuters poll also found that support for Democrats among millennials aged 18 to 34 “slipped by about 9 percentage points over the past two years.” In addition, the extensive Reuters survey found that millennials are increasingly saying that “the Republican Party is a better steward of the economy.”

Reuters interviewed “Terry Hood, 34, an African-American who works at a Dollar General store in Baton Rouge.”

Hood told the outlet that though he voted for Hillary Clinton in 2016, he was open to voting for a Republican for Congress in the midterms “because he believes the party is making it easier to find jobs and he applauds the recent Republican-led tax cut.”

“It sounds strange to me to say this about the Republicans, but they’re helping with even the small things,” Hood told Reuters. “They’re taking less taxes out of my paycheck. I notice that.”