TAMPA — The turnout for Tuesday's election was exactly what many Hillsborough County officials hoped for when they proposed a referendum to raise the sales tax by a half-cent to pay for transportation needs.

Participation was high — 72 percent — and it strongly favored Democrats.

Just one problem: The referendum wasn't on the ballot.

Twice this summer, the county commission narrowly voted against asking residents to raise the sales tax, first rejecting a 30-year surcharge and then a 20-year proposal. If it had passed, it could have brought in up to $117 million a year for transportation.

Backers of the referendum now lament what they see as a missed opportunity to capitalize on an electorate they believe would have viewed the referendum favorably.

Before it failed, proponents said internal polls showed support as high as 65 percent. And it had backing from business groups like the Greater Tampa Chamber of Commerce.

"When I saw Hillsborough County vote for Hillary Clinton, when I saw Hillsborough County elect a new Democratic state attorney, when I saw those types of votes, I truly believed that if it was on the ballot we would've passed it," County Commissioner Les Miller said.

Of course, that's easier to say now. It's entirely possible Hillsborough's proposal, dubbed Go Hillsborough, would not have survived a negative campaign and grassroots opposition from anti-tax and anti-rail factions, just as they helped defeat a 2010 referendum and a similar 2014 ballot initiative in Pinellas County. It faced headwinds, too, from some traditionally liberal groups who felt the proposal lacked a substantive transit investment.

The Hillsborough County Sheriff's Office also investigated whether political connections influenced how the county awarded a $1.3 million Go Hillsborough public outreach contract. The investigation largely exonerated the players involved, but the proposal emerged damaged from the affair.

"In theory, are people in favor of transportation? Yes. Do they think there's a transportation problem? Yes. Did they like Go Hillsborough? No," said Bill Carlson, a Tampa public relations executive who helped rally opposition to the sales tax proposal.

"Right now, it's just a lot of sour grapes. The people who promoted it are trying to blame the people who were against it. They're not to blame at all. They thought it was done in an inappropriate way."

Both sides now want to move forward, and transportation is expected to remain at the top of the county's agenda.

After rejecting the referendum, commissioners settled on a plan to instead spend $600 million in the existing budget on roads and intersections over the next decade. It was largely viewed as a stopgap measure to address a backlog of much-needed maintenance work.

Democrat Pat Kemp, a vocal transit advocate, will join the commission later this month after winning Tuesday's election with a strong 55 percent of the vote. She said her performance here — even better than Clinton's — will embolden her to push for more money for rail, buses and ferries.

"That is a message I've carried strongly," said Kemp, a Go Hillsborough critic. "I did well because that is what our voters are interested in."

The Hillsborough Area Regional Transit Authority, the government agency that operates the county bus system, is doing a transit study to determine what, if any, transit expansions are feasible.

Commissioner Sandy Murman, who won re-election Tuesday, and other Go Hillsborough opponents have said this study could provide the comprehensive plan and vision to take to voters for a sales tax referendum in the future.

As demonstrated by Tuesday's election, Hillsborough is inching from purple to blue in ways that should embolden leaders to push for it sooner rather than later, said Beth Leytham, the public relations consultant who worked on Go Hillsborough.

"You can't go back, but I do believe it would've passed," Leytham said, "And what we just saw gives you a really good reason to look at 2018 instead of 2020."

Contact Steve Contorno at scontorno@tampabay.com. Follow @scontorno.