President Biden and the other national leaders gathered for the Group of 20 summit formally endorsed a new global minimum tax on Saturday, capping months of negotiations over the groundbreaking tax accord. The new global minimum tax of 15 percent aims to reverse the decades-long decline in tax rates on corporations across the world, a trend experts say has deprived governments of revenue to fund social spending programs. The deal is a key achievement for Treasury Secretary Janet Yellen, who made an international floor on corporate taxes among the top priorities of her tenure and pushed forcefully for swift action on a deal. Nearly 140 countries representing more than 90 percent of total global economic output have endorsed the deal. The minimum tax will be coupled with a broader change to global taxation intended to prevent countries and companies from undercutting the new floor. Under the pact, corporations trying to evade taxation by shifting profits to low-tax countries will face a "top-up" tax, which would require them to pay the difference between the tax haven's tax rate and the 15 percent minimum tax rate of the companies where they are headquartered. Supporters of the deal are also optimistic companies will not move to relocate their headquarters abroad, in part because so much of the world has committed to the new minimum. Treasury officials have said new "enforcement provisions" will impose tax penalties based in countries refusing to join the deal.