Mitt Romney’s choice of Paul Ryan to be his running mate is — do I dare say this? — good news for lots of people. Conservative Republicans will mobilize around a deeply conservative Tea Party hero, who will help ease their essential discomfort with their presumptive presidential nominee. Democrats will try to make political hay over the shrink-the-government budget proposals that Ryan, a congressman from Wisconsin, has rolled out in the House, starting with his plan to “save” Medicare by essentially creating a voucher program that would inevitably cause seniors to pay for more of their own health care.

But, most important, it seems to me that the Ryan pick creates the potential for the country to have the debate, in a national election, that it needs to have about the size and role of the federal government.

Ryan is, in many ways, the perfect Tea Party standard-bearer. He is likable, engaging, wonkish and smart. Although the Tea Party is fueled largely by anger, Ryan comes across as a firebrand without the heat. His personal story — with the death of his father forcing him to become self-reliant early in life — is inspiring. He is willing to sit down and talk to anyone, friend or foe, about his ideas. He has the ability to make his radical ideas sound reasonable.

On the one hand, talk about limiting the federal government and shrinking the deficit has been central to Republican rhetoric for years. On the other hand, historically, most Republicans haven’t really meant it. George W. Bush, for instance, pushed for a prescription drug benefit for Medicare recipients that added an estimated $300 billion to the federal deficit — not to mention two budget-busting wars.

Ryan, however, means it. What sets him apart is that he is the rare politician who has been willing to put meat on the bones so that everybody can see what he has in mind. Ryan’s budget plan would reduce the size of government from the current 24 percent of gross domestic product to around 20 percent of G.D.P. The ax would fall most heavily on programs for the poor. As the opinion writer Matt Miller put it recently in The Washington Post, “Over time, Ryan’s ‘vision’ would decimate most federal activities beyond Social Security, Medicare and defense.”

Simply dismissing these ideas as crazy is a mistake. There are many people in the country who agree with Ryan — as they showed two years ago, when they elected 87 Republican freshmen, many of them Tea Party-backed political novices, to the House of Representatives, who went to Washington vowing to shrink the federal government. Although they have had only marginal success so far, it hasn’t been for lack of trying. Their desperate urgency gave us, among other things, the debt-ceiling crisis, in which they risked putting the government in default rather than give in.

But the debt-ceiling crisis could hardly be called a national debate. Rather, it was a negotiation conducted under dire circumstances, and its resolution merely kicked the can to the so-called fiscal cliff we’ll hit in January, when budget cuts will be imposed across the board unless Congress and President Obama unwind what they agreed to.

Which is why it is so important now to have a substantive debate about both President Obama’s vision of the federal government’s role — and Paul Ryan’s. Mitt Romney, who seems unable or unwilling to go beyond the bromides in his campaign speeches, lacks both the skill and the genuine fervor to have this debate. But, with Ryan on the ticket, it is at least possible. I think the Democrats will win this debate, but we need to have it openly, and nationally — rather than having the shrink-the-government movement conducted as a kind of guerrilla warfare, carried out in lightning strikes like the debt-ceiling crisis.

Ever since the campaign entered the postprimary, preconvention phase, with the two candidates turning their attention to each other, it has been a depressing spectacle. The Democrats have demanded that Romney release more of his tax returns — though we already know all we need to know. (Like every wealthy businessman, Romney works hard to minimize his taxes.) In bashing his role in running Bain Capital, the private-equity firm, the president and his aides have hammered Romney for doing what every company does: outsourcing and layoffs. Meanwhile, Romney and his team harp on the anemic economy — even though the Republicans have spent much of the past two years preventing the president from doing anything about it.

Already the Democrats are turning their fire on Ryan and his budget plan. Fine. He and Romney will punch back. No surprise there, either. But Ryan gives the Romney campaign a central idea about government, and, with any luck, the campaign will offer us a real opportunity to think hard about what kind of government we want.

Plus, I can’t remember the last time I’ve been so eager to watch a vice-presidential debate.