House Democrats will use their majority next year to push comprehensive legislation to increase infrastructure spending and transportation-related taxes to help pay for it. In fact, key Democrats say they want to move a bill out of the House early in 2019 before Washington becomes consumed by the 2020 presidential campaign (at least 10 current House and Senate Democrats could be White House candidates). Addressing the big-picture infrastructure needs of the country is something Republicans and Democrat do agree on, but thorny details are likely to scuttle a bipartisan agreement. Here are four things to know about how the 2018 elections will impact infrastructure policy in 2019.

1. By land. Lawmakers in both parties say the country should be doing more on infrastructure. And there’s a lot to do, starting with fixing roads and bridges, installing new interchanges and widening highways. But political consensus usually breaks down when it comes to how to pay for all this concrete and asphalt.

The Trump administration earlier this year rolled out a $1.5 trillion plan to rebuild the nation’s highways, bridges, railroads and transit systems. But it included only $200 billion in federal money – the rest was supposed to come from state and local governments or by privatizing roadways to leverage non-government investment. The White House didn’t propose any tax increases to pay for the new funding.

The overall plan landed on Capitol Hill with a thud. Democrats believed the $200 billion in federal money was insufficient to meet the need and were skeptical about leveraging private investment. Republicans were mostly petrified Trump would cut a deficit-fueled deal with Democrats that would significantly increase federal spending.

Rep. Peter DeFazio, D-Ore.

Rep. Peter DeFazio, D-Ore., is poised to become chairman of the House Transportation and Infrastructure Committee. He has his own “Investing in America” plan centering on raising the federal gasoline tax by 1 cent per year over 30 years, raising $500 billion to be proportionally dedicated to highways, transit and safety programs.

Other Democrats want to ensure House infrastructure legislation includes modernizing the energy grid and updating natural gas and lead water pipelines.

The challenge for Democrats will be passing a transportation plan in the House that includes increasing the federal gas tax when it’s highly likely such a plan would be blocked in the Republican-controlled Senate. Democrats’ new House majority will be relatively slender, and it will include many first-time lawmakers seeking reelection in 2020 in tossup or Republican-leaning districts. Why would those politically vulnerable freshmen Democrats vote to raise the gas tax if the effort is guaranteed to be blocked in the Senate?

2. By sea. DeFazio, who represents the southern half of Oregon’s coastline, included harbor maintenance and maritime transportation as key planks of his infrastructure plan.

DeFazio highlights bipartisan legislation he has co-sponsored with Rep. Mike Kelly, R-Penn., to ensure proper maintenance of the nation’s harbors. The Harbor Maintenance Trust Fund was created under President Reagan for that purpose, but DeFazio and Kelly say the fund’s revenues are diverted to mask federal budget deficits. That leaves America critically short of funds to dredge U.S. ports to accommodate the larger cargo ships using the newly expanded Panama Canal.

DeFazio was disappointed his provision to shore up the Harbor Trust Fund was dropped from the final version of this years’ water resources reauthorization. He said the bill would be among his top transportation priorities in 2019.

Sen. Roger Wicker, R-Miss.

DeFazio’s maritime priorities could have a potential ally in Sen. Roger Wicker, R-Miss., who is likely the next chairman of the Senate Commerce Committee. Wicker represents the port in Gulfport, Miss., and has previously supported similar legislation to address funding and infrastructure needs at U.S. ports.

3. By air. Although Trump last month signed into law legislation reauthorizing the Federal Aviation Administration for five years and addressing major aviation policy issues, DeFazio wants to go further.

The Oregon lawmaker is pushing a bill that would strengthen the nation’s airport infrastructure by removing a cap on certain fees airports can use to pay for improvements to their facilities.

In addition to airport infrastructure issues, DeFazio’s and Wicker’s committees are expected to review progress on FAA policy reauthorization, the agency’s upcoming regulatory activity on drones, and new passenger service requirements.

4. Will there be a bipartisan deal on infrastructure? Leaders on both ends of Pennsylvania Avenue want one, but there are several big roadblocks they would have to overcome.

First, Democrats and Republicans disagree on increasing the gas tax. DeFazio is proposing a gradual, one-penny-a-year increase while Republicans want to explore a new fee structure based on actual miles driven. Second, Democrats would push for significant new spending on clean energy generation and transmission as well as funding to promote carbon-efficient local transportation programs – priorities likely to be received coolly by Trump and Senate Republicans.

Finally, House Democrats’ aggressive oversight and investigations of the Trump administration will likely poison the political environment and make any bipartisan policy agreement exceptionally difficult to achieve.