MILWAUKEE — For months, the Republican presidential race has been animated by the party’s inchoate anger about the state of the country and an equally undefined hope that a candidate would emerge who could usher in an era of civic renewal. But the debate here and its aftermath marked an abrupt transition from vague promises about making America “great again,” in Donald J. Trump’s phrase, to a new season of the campaign shaped more by the glaring policy fissures that are dividing Republicans over what exactly to do about the nation’s problems.

From immigration and bank regulation to taxes and national security, the robust seminar on the issues that began Tuesday night and continued Wednesday exposed a contentious dispute over what it means to be a conservative and offered a preview of the contours of the battle for the Republican nomination.

Years’ worth of arguments conducted at issues forums and in the pages of policy journals and newspapers are now coming to life. The Republican hopefuls are sparring over such high-fiber fare as tax policy: whether to adhere strictly to the party’s supply-side creed or move at least modestly toward policies aimed at bolstering lesser earners. They are clashing over the role America plays in the world, and whether fiscal conservatism is compatible with a drastically enlarged military.

Most vividly, and perhaps consequentially, they are staking out their ground on immigration, clarifying the divide between restrictionists and pragmatists on an issue that could determine who is the party’s nominee.