Caleb Roope’s company was close to nailing down the financing to build 477 apartments outside San Francisco for senior citizens and working families, counting on the cash to be raised from selling U.S. tax credits it received to develop affordable housing.

Then after Donald Trump, who vowed to slash taxes, won the presidential election, the value of those credits plunged — and the plans fell through. “It was already hard enough to make the projects work, given the construction costs,” said Roope, chief executive officer of the Pacific Companies, an Eagle, Idaho-based builder. “The double whammy of the interest rate pickup and then the tax credit pricing decline has really put a lot of projects in jeopardy.”

The prospect of deep business-tax cuts has roiled a vital, if little known, market that pumps billions into affordable housing each year. The price of such credits has tumbled as much as 15 percent