Still, the skyrocketing price tags have alarmed budget watchdogs, who warn of another trillion-dollar figure: the deficit. They point to Congressional Budget Office figures released earlier this month showing the government is already running a $1.07 trillion shortfall through the first 11 months of the government’s fiscal year. The nonpartisan agency predicts trillion-dollar deficits every year for the foreseeable future.

Those big-ticket proposals are driving candidates to search for more exotic tax increases that can generate the cash needed to at least partially offset the costs. Warren and Sanders are turning to a new wealth tax, for example, while Booker wants to tax unrealized capital gains.

Some of those proposed tax increases are so novel that budget scorekeepers aren’t even sure how to estimate how much revenue they’d raise. Two of the nation’s most prominent economists, former Treasury Secretary Larry Summers and University of California economist Emmanuel Saez, have been jousting for months over Warren’s wealth tax, with Summers accusing Saez of vastly overestimating how much it would produce.