Obama aides told POLITICO that when he releases his final budget request next week, the president will propose more than $300 billion worth of investments over the next decade in mass transit, high-speed rail, self-driving cars, and other transportation approaches designed to reduce carbon emissions and congestion. To pay for it all, Obama will call for a $10 “fee” on every barrel of oil, a surcharge that would be paid by oil companies but would presumably be passed along to consumers.

There is no real chance that the Republican-controlled Congress will embrace Obama’s grand vision of climate-friendly mobility in an election year—especially after passing a long-stalled bipartisan highway bill just last year—and his aides acknowledge it’s mostly an effort to jump-start a conversation about the future of transportation. But by raising the specter of new taxes on fossil fuels, it could create a political quandary for Democrats. The fee could add as much as 25 cents a gallon to the cost of gasoline, and even with petroleum prices at historic lows, the proposal could be particularly awkward for Hillary Clinton, who has embraced most of Obama’s policies but has also vowed to oppose any tax hikes on families earning less than $250,000 a year.

During Obama’s first year in office, he was so concerned about the politics of taxes that he scuttled a Democratic transportation bill just to avoid a debate over a gasoline-tax hike. Now in his last year in office, he seems to be actively courting a similar debate.