Hillary Clinton’s new barrage against Bernie Sanders, the Democratic presidential primary opponent she has all but ignored through most of her campaign, is having an effect — though probably not the one she intended.

Sanders’s underdog campaign said it is seeing a surge of contributions as a direct result of the new attention it is getting from the Democratic front-runner, with money coming in at a clip nearly four times the average daily rate reported in the last quarter of 2015.

In its email appeals for money, the campaign accused the Clinton campaign of making “vicious and coordinated attacks” on Sanders’s health-care plan, which calls for a government-run system. Sanders’s strategists are also considering rolling out advertising beyond the early-contest states where it is airing spots now.

The former secretary of state and her team have stepped up their criticism of Sanders on a variety of fronts in recent days as polls have begun to show him edging even with her in Iowa — and, for the first time, looking competitive in a national poll. But the Clinton strategy may be backfiring in some ways.