It remains to be seen how the voters will react to Mitt Romney’s choice of running mate, but one thing is certain: no politician better represents the conflict between the aspirations and the reality of the modern Republican Party better than Paul Ryan.

The Wisconsin congressman has devoted his career to striking a difficult balance: bringing the promised benefits of the federal welfare state in line with the country’s historic tax burden. While this seems straightforward enough, in practice both Republicans and Democrats have wanted to avoid the trade-offs involved.

Democrats argue that ever-growing spending commitments will only require additional tax dollars from the wealthiest 1 percent. Republicans assert that taxes can remain low so long as waste, fraud, and abuse are removed from government spending. The predictable result of this mathematically challenged policy mix has been chronic deficits, now swelling to unsustainable levels.

So Ryan has tried to tackle the biggest long-term drivers of the national debt, which also happen to be the popular entitlement programs considered the “third rail” of American politics. Touch them, legend and recent history have it, and your political career will die. Ryan has made this thankless task more complicated still by stipulating that his reforms have to be politically possible and arithmetically sound at the same time.

There are legitimate, often technical disputes as to whether Ryan’s plans pass either of these tests. But there is little doubt Ryan has outlined some of the most detailed budget and entitlement reforms of any major political figure who is both influential and subject to the whims of the voters. Ryan even represents a congressional district in a swing state that voted for Obama in 2008.

Over the past decade, Ryan has risen to the chairmanship of the House Budget Committee while championing deep cuts in discretionary spending and gradually converting Medicare into a premium support system. What started as the Ryan-authored “Roadmap for America’s Future,” much admired by free-market think tanks but with few congressional supporters, became with some modifications the official budget document approved by the full House of Representatives.

Even in the Democratic-controlled Senate, Ryan’s budget has received more votes than the other alternatives. Only Pennsylvania Republican Sen. Pat Toomey’s proposal—which relies on Ryan for Medicare reform—did better. Obama’s spending plans were rejected 99 to 0. Unlike the House, the Senate hasn’t passed a budget in over 1,200 days.

In a relatively short time, Ryan has not only built a national GOP fiscal policy consensus, he has become it ablest and most articulate defender. And unlike many other green-eyeshade Republicans, Ryan connects what looks like austerity to jobs and economic growth. Romney had already endorsed the principles behind Ryan’s plans. Now he has their best salesman on the ticket.

Those are the Republican aspirations: limited government, a manageable debt-to-GDP ratio, solvent federal programs, and rapid economic growth. But on most of these counts, the record and the reality have been different. The George W. Bush years in particular were characterized by persistent overspending and only episodic growth.

Back then, Ryan was following a very different roadmap. He not only voted for but helped pass Medicare Part D, the prescription drug benefit that was the largest new entitlement since the Great Society and which added trillions to the rickety healthcare program’s already considerable unfunded liabilities. He passionately exhorted his House Republican colleagues to vote for the Troubled Assets Relief Program (TARP) and then was one of only 20 to actually do so. Ryan supported bailing out the auto industry as well as Wall Street.

Nearly everyone who knows Ryan believes he is genuinely passionate about parting the sea of red ink threatening to engulf the country. He took the political risk of associating himself with a far-reaching Medicare plan even before Obama was elected. Yet he voted for most of the big-government initiatives of the Bush era. Ryan still argues that these were the least bad of the available unpleasant options, telling the New Yorker that the period made him “miserable.”

Ryan is less conflicted about his votes for the unfunded Iraq War and the Patriot Act, followed up with Libya war funding and the National Defense Authorization Act under Obama. The Weekly Standard’s Stephen Hayes—who was one of the few journalists privy to the Ryan pick before the news broke—reported that Ryan has in recent months been briefed by Elliot Abrams and “surge” architect Robert Kagan. Eli Lake confirmed in a Daily Beast story with the subhead, “Romney’s VP pick tilts his ticket closer to the neocons on questions about America’s role in the world.”

Like many Republicans, Ryan moves easily from the fact that national defense is the federal government’s preeminent constitutional power—and most fundamental moral duty—to the belief that the fatal conceit stops at the water’s edge. But he is most interested in domestic policy, and he can count. In a generally hawkish speech to the Alexander Hamilton Society, Ryan acknowledged the country’s fiscal challenges could sap its military power and counseled “a healthy humility about the extent of our power to control events in other regions.” (Though he also suggested that retrenchment means “we should reduce ourselves to membership on a long list of mediocre has-beens,” which is rather short on healthy humility.)

How much influence would Ryan really have in a Romney administration? Dick Cheney’s power was unusual and probably unprecedented, owing to his status as an elder statesman who served under a president who was detached from policy details (neither attribute would apply to Ryan). Even in his case, the results were mixed. Cheney certainly left a mark on the Bush administration’s foreign policy and was a much more eloquent defender of the Iraq War than the commander-in-chief.

Yet the war itself was still unpopular and Cheney became one of the most hated figures in the administration. He was largely sidelined during the second term. There are many more examples of Republican administrations employing more conservative vice presidents to please the base in the absence of delivering tangible results to the right. That was Richard Nixon’s role under Dwight Eisenhower, Spiro Agnew’s under Nixon, Dan Quayle’s under George H.W. Bush, and it was sure to become Sarah Palin’s if John McCain had somehow managed to get himself elected.

A frustrated Vice President Ryan could make some waves if he was unhappy with the pace of government-cutting in a Romney administration. He would enter the vice presidency with far more influence among conservative elites than any of the above figures. Some of that influence is starting to trickle down to the grassroots, as evidenced by the angry Iowa Republican who chewed out Newt Gingrich for calling the Ryan plan “right-wing social engineering.” The fellow bluntly informed the former House speaker, “You’re an embarrassment to our party.” A successful campaign would only improve Ryan’s standing with the Republican rank-and-file.

But there is nothing in Ryan’s record under George W. Bush that should give confidence he would use that leverage. The entrepreneurial, independent Ryan has been much more in evidence since Obama has been president amidst a leadership vacuum in the Republican Party.

Ryan’s contradictions are the GOP’s. The party of limited government, lean budgets, and robust civil society often delivers anything but, except perhaps in comparison to Obama’s banal party of the Life of Julia. The man who has done more than any other member of the Republican leadership team to move the Tea Party from inchoate anti-Obama rage to a potentially achievable policy agenda voted for much of the spending that gave rise to the Tea Party in the first place.

In that sense, Romney’s pick could hardly be improved upon. The question for Ryan is one that faces the party as a whole: If entrusted with power, will you realize your aspirations or repeat your past results?

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