WASHINGTON — Elizabeth Warren’s call for a new 2 percent tax on the wealthiest Americans is so popular among her supporters that impromptu chants of “two cents” routinely surface at her rallies. But Bernie Sanders, Warren’s chief competitor for liberal voters, made clear on Tuesday he also has “a plan for that.”

Sanders, a Vermont senator, announced a plan to tax the nation’s wealthiest households. He vows to go far further than Warren and generate more than $4 trillion over the next decade,  substantially reducing billionaires’ fortunes.

His attempt to take back an issue that has become a signature of Warren’s comes as she’s gaining ground in the Democratic primary while Sanders’ own support appears to be softening. The Massachusetts senator has topped Sanders in recent polls of Democrats in Iowa and New Hampshire that show her running about even with the longtime front runner, former Vice President Joe Biden, in those states.

Both Warren and Sanders are longtime friends who agree on many major policy issues. So far they’ve steadfastly refused to criticize one another while competing to deny President Donald Trump a second term. But the dueling “wealth tax” plans suggest that Sanders may try to take on Warren more directly.