Silvio Berlusconi, who resigned as Italy’s prime minister 15 months ago, is staging an appalling comeback. With less than a week to go before national elections this weekend, polls show that Mr. Berlusconi’s coalition has surged into second place, trailing the center-left coalition by single digits.

While Mr. Berlusconi is unlikely to ever win a fourth term, a strong showing by his forces could make it impossible for any party to form a working parliamentary majority. That would be disastrous for Italy, which needs to push through overdue reforms, like stronger anticorruption laws, a fairer tax code and more competition.

These are not the issues Mr. Berlusconi can credibly run on. Instead, the centerpiece of his campaign has been a populist promise to end the unpopular homeownership tax introduced in 2012 and refund last year’s payments. The housing tax is made necessary by Italy’s poor record in collecting other taxes and the European Union’s perverse insistence on balanced budgets in a recession. But refunding it would punch a huge hole in Italy’s finances and set off an increase in interest rates for Italian bonds, wiping out all the painful sacrifices last year.

This reckless pandering has boosted Mr. Berlusconi in the polls, largely because his rivals have failed to inspire voters. Pier Luigi Bersani, leader of the center-left Democratic Party, is a moderate ex-Communist and former industry minister in the 1990s. To many, he symbolizes Italy’s old political class, out of ideas and out of touch. He is also seen as too beholden to the unions to press labor market reforms. Running third is an anti-politics slate organized by a comedian, Beppe Grillo.