President Obama will use his election-year State of the Union address on Tuesday to define an activist role for government in promoting a prosperous and equitable society, hoping to draw a stark contrast between the parties in a time of deep economic uncertainty. ...Mr. Obama will call for changing the corporate and individual income-tax codes so the wealthy pay more, both to finance government investments and to alleviate the rise in income inequality in recent years. Republican presidential candidates have countered that government should get out of the way.