By Taylor W. Anderson • The Bulletin

A growing number of voters in Oregon are choosing not to register with the state’s two main parties, creating challenges for Democratic and Republican party leaders who want to know which races to focus their resources on as November approaches.

In a year with more unaffiliated voters than ever, predicting what will happen in November becomes an equation with no perfect outcome.

If Tom Powers’ math is correct, Oregon Democrats would not only have another Senate majority for the next two years after this election, they would add to their two-seat control.

Powers, who is executive director of the Senate Democratic Leadership Fund, said internal polling and other data show Senate Democratic candidates might fare well in what’s typically a strong Republican cycle.

The parties create a database of voters who aren’t Republican or Democrat and assign them a score based on the likelihood that they will support Democratic or Republican candidates.

“I think our polling confirms that the Senate map this year favors Democrats and the math favors Democrats as well,” Powers said.

The Senate Republicans’ campaign arm, The Leadership Fund, didn’t respond to a request for comment.

The parties have identified four Senate races that could be key for who controls the Senate for the next two years .

Democrats have an edge in each of those races, Powers and registration data say, but the number of unaffiliated and other voters in every district is large enough to sway each race.

Registered Democrats in the race of Sen. Betsy Close, R-Albany, who was appointed to her seat, far outnumber registered Republicans.

Sen. Alan “Doc” Bates, of Medford, is considered the most vulnerable Democrat, but Powers said he expects independent voters in the district will lean to Bates over his Republican challenger Dave Dotterrer.

Sal Peralta, secretary of the Independent Party of Oregon, said there are more options to consider that make predicting results a guessing game.

“I think that the likeliest outcome in this cycle is that the (Democrats) will pick up one seat in the Senate and the (Republicans) might pick up one or two in the House,” Peralta said.

Republican candidates also won the Independent Party nomination in many of the close Senate and House races. Peralta said voters who aren’t familiar with legislative races might see the Independent label on the ballot and vote for that candidate.

Peralta said the Independent Party nomination that many Republican candidates will carry on the ballot should help them offset some of the registration imbalance.

Republicans also vote in mid-term elections at a significantly higher rate than Democrats in Oregon.

Historical data from midterm elections show about 74.3 percent of registered Oregon Republicans vote in nonpresidential elections. That’s higher than the Democrats’ 71.6 percent average turnout since 1998.

Jim Moore, a political science professor at Pacific University, said unaffiliated voters tend to break evenly into the registration numbers of both main parties.

“If we look at a state Senate district that is 40 percent Democratic and 35 percent) Republican, the (unaffiliated voters) are going to break just about that way,” Moore said.

Oregon’s Democratic Party lost 1.4 percent of its registered members from 2010 to July 2014, while the Republicans added nearly a percent. But the bloc of voters who don’t belong to any party has jumped 16 percent in that time.

— Reporter: 406-589-4347,