PORTLAND, Ore. (AP) — Oregon voters are facing a familiar theme on their primary ballot Tuesday — well-financed Democratic incumbents looking to slide past little-known challengers while Republicans attempt to nominate candidates who could put up a fight in November in a heavily blue state.Much of the Election Day drama will center less on candidate races and more on a referendum seeking to repeal a bill passed last fall by the Democratic-controlled Legislature that raised the state gas tax and hiked a series of fees.The legislation was Democrats’ answer to help Oregon’s transportation budget as the state projects a decline in gas tax revenue from the shift to more fuel-efficient, electric and hybrid vehicles. The gas tax is the largest funding source for fixing roads and upgrading highways.The referendum, known as Measure 120, lands on the ballot as the cost of gas is spiking nationwide from the war in Iran. The state’s Democratic governor, Tina Kotek, and other lawmakers from her party have acknowledged it will be tough for the ballot measure to pass. A yes vote means voters approve of the gas tax increase while a no vote means they reject it.“It’s going to lose, so we might as well get on to the work of finding alternatives,” said Democratic state Rep. Paul Evans, anticipating that voters will reject the gas tax increase. “It has been a frustrating year.”