Senate Republicans approved a $4 trillion budget measure Thursday, taking a crucial step toward their goal of passing a tax plan this year.

The chamber approved the budget resolution by a 51-49 vote. Sen. Rand Paul, R-Ky., was the only GOP senator to vote against it.

Senators will now have to reconcile their budget resolution with a separate one passed by the House. The other chamber could simply choose to pass the Senate budget blueprint.

Passing a budget unlocks reconciliation, which enables the GOP to pass a tax bill with a simple 51-vote majority in the Senate. Using the tool removes the need for winning Democratic support, which would likely sink a GOP tax measure.

Republicans have described overhauling the American tax system as crucial to achieving campaign promises and avoiding an electoral setback next year. Disagreements within the party already derailed one key campaign plank, repealing the Affordable Care Act.