WASHINGTON—Former White House cost-cutting czar Elon Musk called President Trump’s “big, beautiful” tax and spending package a “disgusting abomination,” stepping up his criticism just as the Senate is trying to quickly pass the measure and get it signed into law by July 4.

Musk, who officially left the White House last week, appeared to be pointing to estimates from budget experts who found that the Republican tax bill could add more than $2.5 trillion to the federal deficit in the coming years.