While running for the Texas Republican senatorial nomination, Ted Cruz signed a pledge to vote against unbalanced budgets, new spending unless offset by cuts elsewhere, and any increase in federal borrowing. His opponent, David Dewhurst, added his signature shortly afterward.

The Cruz-Dewhurst race was one of the most contentious Republican primaries in the country, but the substantive differences between their respective platforms were relatively minor. Even the columnist George Will, who has repeatedly praised Cruz in print, conceded: “On 99 percent of U.S. Senate business, Cruz and Dewhurst probably would vote alike.”

Many Tea Party conservatives are still more demanding. When Sen. Robert Bennett was ousted by the Utah Republican state convention, and ultimately replaced by constitutionalist Mike Lee, his lifetime American Conservative Union rating was 83.6 percent. That was better than the last two members of Congress the GOP nominated for president, yet it wasn’t good enough.

Cruz himself once told this writer, “If I go to Washington and just have a good voting record, I will consider myself a failure.” Such an attitude isn’t merely ideological chest-beating. Just to repeal President Obama’s Affordable Care Act, to say nothing of restoring constitutionally limited government, will require Republicans to do things in office they’ve proved unwilling to do before.

Judging from the ratings of groups like the American Conservative Union, congressional Republicans have become more conservative over time. Yet the government keeps getting bigger. It took 200 years before the federal budget reached $1 trillion—under a Republican president, natch—and now deficits of that size are the norm.

Republicans bitterly oppose each successive wave of Democratic legislation, but few entrenched liberal policies are ever reversed once enacted. The two major exceptions: welfare pre-Clinton and marginal tax rates pre-Reagan. (And even in those cases, federal welfare programs and the progressive income tax endured.) A Republican Congress dramatically cut farm subsidies, but they were restored by a future Republican Congress.

Things are even worse when Republicans control the White House. Under Ronald Reagan and George W. Bush, the GOP cut taxes. Under neither president did Republicans cut spending; during the Decider’s reign, they didn’t even try. Instead Republicans created the biggest new entitlement since LBJ’s Great Society, grew the Education Department they once pledged to abolish, and added a new Cabinet agency with redundant functions to boot.

Repealing Obamacare, reforming Social Security and Medicare, reducing the debt-to-GDP ratio to a manageable level, even balancing the federal budget within our lifetimes are objectives that cannot be achieved without Republicans who are as serious about cutting government as Democrats are about growing it. Right now, a little bit of extremism in defense of liberty really is no vice.

As evidenced by Dewhurst’s copycat pledge-signing, candidates like Cruz push the Republican Party to the right simply by fostering competition for the conservative mantle. But that by itself isn’t sufficient to make the party genuinely fiscally conservative. Are these candidates more serious about limiting government than their predecessors?

Until recently, even the most conservative Republican leaders on Capitol Hill were New Right populists. Jesse Helms, the most consequential conservative legislative champion since Barry Goldwater, cared most deeply about social issues. Newt Gingrich was a technocrat who wanted government to be more efficient and Republican-friendly, not smaller. Tom DeLay wanted to push K Street to the right, not to limit its influence on Main Street. The only real government-cutter near the top of the ‘90s GOP congressional leadership was Dick Armey, who was frequently marginalized and would later admit to helping to pass bills he personally thought unwise.

Most of these conservative leaders disdained liberal welfare spending but they were perfectly happy to spread the wealth to Republican constituencies like the military, business owners, and farmers. Culturally Southern, they took their government nationalistic and moralistic rather than small. Even the exceptions, such as Armey and his fellow Texan Phil Gramm, were generally more willing to tolerate big government under Republican presidents.

The conservatives of the Tea Party era are still disproportionately Southern, but their emphasis is different. South Carolina Sen. Jim DeMint voted against the Medicare prescription drug benefit and No Child Left Behind while in the House, defying the Bush administration and the GOP congressional leadership. So did Jeff Flake, the Arizona Republican running to join DeMint in the Senate. They are social conservatives, but see the national debt as the paramount moral issue.

Cruz lacks their legislative voting record, but it is nonetheless intriguing that he wrote his senior thesis at Princeton on the Ninth and Tenth Amendments—two neglected parts of the Bill of Rights that are the key to reasserting limits on the federal leviathan. Mike Lee wrote a book straightforwardly arguing that most post-New Deal federal programs, including the big entitlements, are effectively unconstitutional. Rand Paul is both the literal and figurative son of the most successful libertarian politician in modern times.

In the past, the Republican caucus’s most ardent budget-cutters tended to be House backbenchers. Now they are senators, a distinction that comes with far more prestige, media attention, and procedural power. With time, any one of them could launch a credible presidential campaign. Paul and Lee won their seats by beating Republicans who were insufficiently committed to shrinking government; DeMint has devoted much of his career to supporting such primary challenges.

The presence of identifiable leaders like Paul and DeMint, who have defined themselves in opposition to big-government Republicans as well as Democrats, could keep congressional conservatives from going off-track the next time the GOP wields power. They can also reinforce one another. Since Paul joined the Senate, DeMint has voted to revoke authorization for the Iraq War and to oppose the National Defense Authorization Act, two stands that would have been unthinkable three years ago. Lee has sided with Paul on the Patriot Act and U.S. military intervention in Libya.

Even with a growing Paul-DeMint caucus in the Senate, there is always a risk that the GOP’s small-government fervor will once again prove evanescent. We’ve seen Republicans who decried Hillarycare as a socialist plot embrace Romneycare and Medicare Part D. We’ve watched them oppose war in Kosovo and then cheerlead for it in Iraq. What will today’s Obamacare opponents favor tomorrow? Will those who were against intervening in Libya march to Iran and Syria?

For the liberty movement—perhaps best understood as the Ron Paul-inspired, libertarian-leaning wing of the Tea Party—the dilemma is most acute. Like the Christian right before it, they must try to be effective in changing the Republican Party without being changed by it. Only time will tell whether the new Republicans shrink government or grow in office.

W. James Antle III is associate editor of The American Spectator and a contributing editor of The American ConservativeFollow him on Twitter.