(CNN) - It's become an old cliché that elections "come down to turnout." While that may be exaggerated in most places, it's definitely not in Texas. Democrats need voters who don't traditionally vote to cast a ballot this year in order to to win, and it's not clear that they will in 2018. This could cost Democrats on both the Senate and House sides.
A new Quinnipiac University poll of the Texas Senate race finds Republican Sen. Ted Cruz leading Democrat Beto O'Rourke by a 9-point margin. That's Cruz's best poll in over two months, and an increase from his 6-point advantage last month in the Quinnipiac University poll.
Some of this change could be statistical noise, but Quinnipiac also changed the population it was polling between surveys. They went from registered to likely voters.
Not all voters actually cast a ballot in an election. That's why it's important to poll the subset of voters who actually will.
Most public pollsters shift to likely voters around this time as it becomes clearer who is going to vote in the midterm the closer we are to an election. That's especially the case for pollsters who don't rely on a voting list such as Quinnipiac to know how often people have voted in the past.
The shift to more pro-Republican results among likely voters isn't surprising, but has to be disappointing to Democrats.
Historically, the likely voter electorate in Texas is less friendly to Democrats than the registered voter electorate.
The shift appeared to impact other questions as well. President Donald Trump's approval rating is up 3 points from last month in the Quinnipiac poll of Texas, despite his approval rating falling nationally during the same period.
Back in 2016, then Democratic President Barack Obama's net approval rating (approval - disapproval rating) dropped 6 points when Marist College went from registered to likely voters in Texas. That was the largest decline in any state polled by Marist in the final month of the campaign, and it probably hurt Democrat Hillary Clinton in the state.
The drop is in large part because of the demographic makeup of likely versus registered voters in Texas. The government's Current Population Survey found that the electorate that cast a ballot in 2016 was 3 percentage points more white than the entire registered voter electorate. That was tied for the largest increase in the entire nation for white percentage going from registered to actual voters.
There had been some hope among Democrats that O'Rourke's candidacy might drive higher turnout, which could, in turn, help Democrats in the key congressional races. It's not clear that's happening yet.
For example Republican Rep. John Culberson is currently ahead by 2 points in a new Siena College poll of Texas's 7th Congressional District. Culberson isn't being helped Cruz. Cruz is down 51% to 44% in the district.
O'Rourke, though, doesn't seem to necessarily be driving higher turnout among Democrats.
Culberson is benefiting from an electorate that is fairly favorable for Republicans. Among all registered voters in the district Culberson is actually trailing by 7 points. He's even down 2 points if the electorate resembles the one that came out to vote in 2016. In other words, the electorate, at least in the 7th, is projected to be worse for Democrats than it was in 2016.
Now, these are just two (Quinnipiac and Siena) polls. There's still over a month before the election. Likely voter model and screens may, for whatever, reason not be picking up Betomania. There are lots of ways to build a likely voter screen or model, and the ones being chosen by these pollsters may not work this year.
But keep in mind, most pollsters are talking to lower propensity voters that O'Rourke may be attracting. It's just that right now these pollsters see no reason to believe that the electorate will be pro-Democratic compared to two years ago.
That is, there's reason to believe that the worst fears of Democrats in Texas (low voter turnout) could still come true.
Copyright 2018 by CNN NewSource. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.