WASHINGTON — As President Trump’s top economic advisers faced a barrage of questions on Wednesday about the tax plan they had just unfurled, there was one that they struggled most to answer: how to keep the “massive tax cuts” they proposed from ballooning the federal deficit.

The White House insists that economic growth will cover the cost, which could be as high as $7 trillion over a decade. But the question will dog Republicans and could fracture their party as they face the prospect of endorsing a plan that many economists and budget analysts warn will increase the deficit. After years of fiscal hawkishness, conservatives now face a moment of truth about whether they truly believe America’s economy is drowning in debt.

Some skeptics are already ringing alarm bells, fearing that Republicans will sign on to what critics see as a dangerous plan composed by a president who called himself the King of Debt.

“It seems the administration is using economic growth like magic beans: the cheap solution to all our problems,” said Maya MacGuineas, president of the Committee for a Responsible Federal Budget, a nonpartisan group that advocates fiscal restraint. “But there is no golden goose at the top of the tax-cut beanstalk, just mountains of debt.”