WASHINGTON—Elon Musk gave new fuel to GOP critics of the Republicans’ multitrillion-dollar tax and spending agenda, saying that the current measure failed to reduce the federal deficit, echoing complaints from hard-line factions in both the House and the Senate.

President Trump’s “Big Beautiful Bill,” a major tax and spending package, narrowly passed the House of Representatives before Memorial Day but now faces a highly uncertain future in the Senate. -Senate Republicans are planning to rewrite the legislation due to internal divisions between moderates and conservatives over key provisions,