Though it wasn't the filibuster heard round the world, it certainly reverberated around Washington. Rand Paul's nearly 13-hour talkathon not only extracted from the Obama Administration a rare constitutional limit to executive power, it made the senator from Kentucky a conservative hero and breathed new life into the movement that helped elect him.

But which movement was that? Everyone noted the similarities between this old-fashioned filibuster and the one in Mr. Smith Goes to Washington, the classic Frank Capra movie. What the newly appointed Senator Jefferson Smith (played by Jimmy Stewart) achieved through innocent grit, Senator Rand Paul accomplished by courage and guile. I give him credit for both. Paul was elected, after all; he's a politician and the son of a politician.

As a member of the Senate class of 2010, he was one of the leaders of the Tea Party, the citizens' movement that rose up to defend the Constitution and to oppose President Obama's long train of abuses and usurpations. Marco Rubio, Ted Cruz, and other stalwarts supported Paul on the Senate floor. The episode amounted to an unexpected recrudescence of the Tea Party, which in effect launched a populist filibuster on behalf of the rule of law, and won.

Yet Paul is also a libertarian, and the son of one. His newfound prominence therefore set off alarm bells. Senator John McCain said his colleague's foreign policy views made him one of the party's "wacko birds." Bill Kristol cautioned Republicans against "embracing kookiness" and "pseudo-constitutionalist paranoia," and wondered if it would serve Paul's own interest to be "the spokesman for the Code Pink faction" of the GOP?

The answer, presumably, is no, and one test of Rand Paul's seriousness will be if he transcends the family fixation with "blowback," the notion that America brought 9/11 and the resulting war upon itself, as Muslim revenge for its highhandedness in the Mideast.

In the long run, however, and likely even in the short run, it is domestic policy that will determine what kind of country we shall be. On this front, though wrong about many things, libertarians have been right for a long time about something very important: the modern state's tendency to unlimited government. The progressive state loosens all the salutary restraints of the old Constitution by concentrating more and more government powers in the hands of self-declared experts, who can do unlimited "good" for us—and to us. Spend a century, as progressives have, disdaining the Constitution's impediments to social engineering, and you wind up with a liberal administration that has to be badgered into the grudging admission that, no, the Constitution does not permit the president to kill American citizens just because he thinks they need killing.

Unlimited ambitions breed unlimited spending. The Republicans in the House have offered an alternative to this madness. Their champion, Paul Ryan, chairman of the Budget Committee, proposes to end the federal budget deficit in ten years, and with no net tax increases. Nor, curiously, does his plan contain net spending cuts: spending will rise at 3.4% a year, rather than the 5% annual rate we face currently. The plan accepts the tax increases already insisted on by the Democrats, including those for Obamacare, even though Ryan assumes the repeal of Obamacare. Medicare reform will not kick into high gear for ten years, and even then will be gradual. Social Security reform is off the table.

No one should underestimate the fiscal and political difficulties of deficit reduction, particularly if undertaken as part of re-limiting the federal government. Ryan has run this minefield before, and he knows the hazards. Still, laudable as his plan is, one wonders if we can do better.

Senator Rand Paul has a proposal to balance the budget in five years, not ten. He hasn't talked about it much, preferring to gnaw away at foreign policy. The details are presumably sketchier than in the House plan. But this is a debate that the country needs to have soon, and that the Republican Party alone is capable of having right now: how low can federal spending go, and how fast?

I saw an amusing answer on an old bumper sticker: There's no government like NO GOVERNMENT! But that is anarchism, not libertarianism, and certainly not constitutionalism. The question is what a responsibly but aggressively trimmed federal budget—one that is sufficiently viable politically to point the way for the GOP, one that could breathe fresh life into constitutional limitations—would look like.

It may be that such a plan would not be Rand Paul's at all, nor certifiably libertarian. Maybe it would be called the Cruz plan, the Rubio model, the Jindal proposal…or simply the Tea Party budget. But it could be immensely clarifying, and could change the terms of the discussion, on and off the Senate floor.