WASHINGTON — President Trump’s failure to push through the broad health care overhaul he promised has raised questions about the prospects of a sweeping rewrite of the tax code. It is a politically fraught and dizzyingly complex endeavor that pits powerful interests against one another and threatens to increase the federal deficit.

“Trump has to win on this,” said Stephen Moore, a distinguished visiting fellow at the Heritage Foundation who advised Mr. Trump on tax policy during his campaign and transition. “There’s no margin for error here, and failure is just not an option.”

Just how difficult will it be? Here are five obstacles to getting a new tax law:

A leadership vacuum

The greatest hurdle to a tax overhaul may be the White House itself. Mr. Trump has yet to make basic decisions about the structure and scope of his plan, the strategy for pushing it through Congress or even who in his administration will be in charge of crafting and selling it. While White House officials said they would unveil a plan weeks ago, one has not materialized.

“Obviously, we’re driving the train on this,” Sean Spicer, the White House press secretary, told reporters on Monday as he deflected basic questions about what the president’s proposal would look like. That is hardly obvious to many members of Congress, administration insiders and outside observers who now question whether Mr. Trump and his close advisers are capable of executing on such an ambitious and high-stakes negotiation.