President Trump's endorsement of suspending federal gas taxes pushes the idea higher on the political radar, but it still faces long odds.Why it matters: Some Republicans rushed to introduce bills, and a few Democrats have already endorsed the idea — but there are still serious obstacles that could keep Trump's comments from becoming reality.The federal tax is 18.3 cents for gasoline and 24.3 cents for diesel (with another .1 cent fee for addressing leaking underground tanks).A few dynamics to watch following Trump's comments to CBS News...📜 Capitol Hill. Trump needs Congress to act, and the immediate signs are mixed. GOP lawmakers including Sen. Josh Hawley (R-Mo.) quickly promised legislation, but Senate Majority Leader John Thune was noncommittal."I've not in the past obviously been a fan of that idea. But you know I've got some colleagues out there who think it's a good idea and so we'll hear them out," he told reporters.Thune noted the revenue loss could hurt the Highway Trust Fund, and said "the best thing [that] can happen for gas prices is for the [Strait of Hormuz] to get opened up again."💪 The White House political operation. It's hard to know whether it's something Trump's team will truly push, or instead one of his frequent musings, or something in between.🗳️ It's a 2028 thing. Several potential White House hopefuls have now pushed to temporarily nix the tax.They would be Sen. Mark Kelly (D-Ariz.), Hawley, and Kentucky Gov. Andy Beshear.🤷 The politics and plans remain in flux. Senate Minority Leader Chuck Schumer (D-N.Y.) isn't exactly shooting down the idea, but in a floor speech Monday, he took the position that it's not enough."[L]et's not pretend 18-cents of gas tax relief per gallon makes up for the damage Trump created with this war," Schumer said. "Eighteen cents isn't a dollar-fifty — which is how much the price of gas has gone up since the war started.""The best way to lower costs is to end this illegal war."Aides to House Speaker Mike Johnson (R-La.) and House Minority Leader Hakeem Jeffries (D-N.Y.) didn't respond to requests for comment.💵 The numbers are daunting. One reason a waiver has never happened — despite surfacing often when prices spike — is the budget impact is big even while consumer relief is modest.The revenue effect and loss to the Highway Trust Fund — which supports roads, bridges and transit — depends on the duration and how it's structured.For instance, Kelly's plan would divert other monies to the fund. But a holiday of any length is expensive for Uncle Sam.The research firm ClearView Energy Partners said a hypothetical gas tax waiver from May 15 to Nov. 30 would cost nearly $14 billion. Add in other fuels, and the price climbs a lot more.The bottom line: The high costs and revenue loss for highways "might ordinarily produce lethal sticker shock on Capitol Hill," ClearView said in a client note."But in a mid-term election year where both parties are in no-holds barred pursuit of Congressional control, we cannot wholly rule it out."Sign up here for Axios' Future of Energy newsletter.