Threat of Lower Turnout Looms Over Both Political Parties

— -- Concern that Donald Trump could affect November voting further down the ballot has been floating around some Republican circles for months, but there could be a similar effect across the aisle as the Democratic Party primary drags on.

Sen. Bernie Sanders won the Oregon primary Tuesday night and Kentucky is still too close to call, though Hillary Clinton declared herself the winner there.

Despite Clinton’s significant head start in the polls and her substantial war chest at the beginning of the race, Sanders’ ability to generate such a passionate and devoted following could complicate Clinton’s efforts to attract his supporters as she transitions to general election mode, assuming her delegate lead holds.

James Campbell, a professor of political science at the University at Buffalo, says that the negativity may be more vocal and lead to lower turnout for Republicans, but the Democrats also have cause to worry about their own turnout issues.

"There may not be quite the rancor on the Democratic side, but the disgruntlement of Democrats is greater among a group of young prospective voters whose turnout rates are historically low to begin with,” said Campbell, whose book on political polarization is scheduled for release this summer. “Unless they can be energized, there may be a lot of Democratic no-shows as well.”

But Hans Noel, a Georgetown University associate professor, told ABC News that one of the "biggest" things Sanders has done to help the Democrats is energize the base, which could lead to more votes for whoever becomes the party's nominee.

"He’s gotten a lot of new voters energized and registered, and they care about what happens in the general election,” Noel said. “There’s good reason to believe they will turn out for the Democrat in November, as they are reminded of the contrast between Clinton and Trump.”

The Sanders campaign has been touting a similar point, with senior adviser Tad Devine telling ABC News that more than 900,000 people have registered to vote or changed their registration in California as the state's June 7 primary approaches.

When it comes to bringing people to the polls, Clinton and Trump both have a lead on Sanders, overall. So far, Clinton has won 13,036,950 votes, Trump has won 11,148,252 and Sanders has won 9,788,804.

In Oregon's primary, the Democrats drew 181,629 more votes than the Republicans.

Both Sanders and Clinton drew more votes than Trump, with Sanders winning with 273,376 votes and Clinton trailing with 226,086 votes. Meanwhile, Trump won 212,457 votes.

That Democrats had a higher turnout in the state overall is not surprising: the last time the state went for a Republican president was in 1984, with incumbent President Ronald Reagan.

Fearing what might come, conservative activists had pushed for a GOP alternative as part of the "Never Trump" movement even before he became the presumptive nominee.

More recently, Sen. John McCain said Trump could cause him turnout problems in his re-election campaign because of the significant Hispanic population in his state, Democrats and Republicans.

"The first wedge that Donald Trump had that gave him a rise was build a wall, rapist, murderers, etc. And ... if you listen to or watch Hispanic media in the state or the country, you will see that it is all anti-Trump. The Hispanic community is roused and angry in a way that I have never seen," McCain said, according to a recording from a private fundraiser in April and obtained by ABC News.

As for some Republicans, rather than necessarily staying at home, they could show up at the polls in November and just avoid the top of the ticket, professor Campbell said.

"No matter what Paul Ryan or any of the other GOP leadership does, there will be many rank-and-file Republicans who will be turned off by their party's presidential nominee,” he said.

“Republican turnout is likely to suffer, but since the problem that many of these Republicans have with their party is directly associated with Trump, I would not be surprised if a good number turned out to vote and voted below the presidential line."