With the next Obamacare enrollment period set to open on Saturday, the Obama administration is hoping to get millions of people who sat on the sidelines last time to sign up for coverage through the law's health insurance marketplaces. But, the strong partisan politics surrounding the health-care law will keep some people from joining the markeplaces, new research suggests.

The analysis, published in the National Bureau of Economic Research, comes from Washington state, one of the earliest states to embrace the Affordable Care Act after its passage. University of Washington researchers sent out mail surveys to 40,000 households in the state between December 2013 and January 2014 — right in the middle of Obamacare's first enrollment period — to gauge interest in the state's insurance marketplace, or exchange, among those potentially eligible.

The researchers asked people to say how certain they were to enroll in the marketplace, and they asked them about insurance status, health needs and their financial situation. Researchers also tried to capture respondents' political views by asking whether they agreed with the 2012 Supreme Court ruling upholding the ACA and which party they believe was responsible for last October's government shutdown.

People who were certain they'd buy from the marketplace — who made up about 7 percent of the approximately 4,000 survey responses — were much more likely to support the Supreme Court decision upholding the law and blame Republicans for the government shutdown, the survey results showed. Researchers found that compared to the insured population in 2013, after adjusting for financial concerns and medical needs, the uninsured were much more likely to enroll through the state's exchange if they thought Republicans or both parties caused the government shutdown.

And this is where politics came into the picture: uninsured people were not more likely to buy from the exchange if they blamed Democrats for the shutdown. So extra outreach efforts could be in order to reach these people, the researchers conclude.

"Alternative strategies, for example bipartisan outreach, may be necessary to convince these groups of eligible beneficiaries to consider enrollment," the University of Washington researchers write. "This is especially true if such dynamics, or possibly even more political divisiveness, persist in those states where a Federal Health Exchange is set up."

That prescription calls to mind an earlier survey finding that Kentuckians were pretty happy with their state-run exchange, but still hated Obamacare. That's a credit to Kentucky's successful branding efforts to separate its insurance marketplace from the federal health-care law.

But it's also hard to imagine, at least in the short term, more bipartisan enrollment outreach in these states with federal exchanges — especially not when the Supreme Court is set to hear a challenge to the subsidies that make insurance more affordable to millions of Americans.