Millionaire Tax Tests a State’s 93-Year Aversion to Income Levy

After nearly a century of trying, Washington state Democrats could finally pass an income tax – a move that would hit 30,000 or so top earners.

A proposed 9.9% tax on incomes over $1 million has a good chance of winning approval in the 28 days left in the state legislative session. The measure would fundamentally change the revenue structure in the state, which is known both as the home of glittering tech wealth and as a rare liberal bastion with low taxes.

The Washington State Capitol in Olympia.

Photographer: David Ryder/Getty Images

Supporters say it’s a long overdue shift away from reliance on the sales tax, which falls ...