An infrastructure plan put together by two advisers of President Donald Trump could carry potential risks, economists and transportation experts say.

The plan is based on a paper by Trump economic adviser Peter Navarro, who is director of the National Trade Council, and Wilbur Ross, Trump’s pick for Commerce Secretary that was set before the election.

The plan recommends allocating $137 billion tax credits for private investors who underwrite infrastructure projects with the goal of spurring $1 trillion in infrastructure investment in the span of 10 years.

But even some Republicans are skeptical that a such a plan would work on a national scale, because without some way like tolls to generate revenue, roads and bridges aren’t attractive to investors.

And while tax credits could attract investors, they could also reward them in some projects that would have been built anyway, economists and transportation experts told The Associated Press.

“I don’t think that is a model that is going be viewed as successful or that you can use it for all of the infrastructure needs that the U.S. has,” Douglas Holtz-Eakin, a former head of the Congressional Budget Office and economic adviser to Sen. John McCain’s 2008 presidential campaign, told the AP.

While some Democrats have expressed openness to working the president on infrastructure, Sen. Bernie Sanders, I-Vt., has called Trump’s proposals “a scam” in the past.