The campaign for the Republican nomination for President of the United States in 2012 reflects the difficulty Republicans primary voters are having with the conservative credentials of the candidates. What is a true American conservative? How do we reliably tell the difference between someone who has the heart and soul of a true conservative and those who wear the conservative label when it benefits them but will find excuses to shy away from it when they are in office? There is one sure-fire test.

Mitt Romney, Rick Santorum, and Newt Gingrich call themselves conservatives. All three, however, have supported policies or voted for legislation when they were in office that was and is anathema to most conservatives. Libertarian Ron Paul makes no pretense that he is a conservative.

Romney’s campaign is dogged by his apparent inability to convince primary voters that he is a true conservative. In his speech at the Conservative Political Action Committee conference he called himself a “severe” conservative, whatever that is. Nevertheless, throughout his political career, Gov. Romney has changed his views many times on important conservative issues; and conservatives decry “Romney Care,” his signature issue as governor of Massachusetts.

Rick Santorum is a social conservative, staunchly anti-abortion and anti-gay marriage; but his critics point out that as a Senator from Pennsylvania he voted against right-to-work laws and voted repeatedly for extensions of the federal spending limit and other large deficit spending bills.

Former Speaker Newt Gingrich’s says he is a conservative, pointing to the “Contract with America,” his winning back the House of Representatives for Republicans in the 1994 election, and the balanced budgets passed by Congress during his tenure. To the contrary, his critics note that he has been a supporter of man-made global warming and programs that would expand, not decrease, the size of government.

Romney, Santorum, and Gingrich all denounce President Obama and Democrats for their progressive, socialistic policies that they say are ruining America; but as they are learning, even the most outspoken anti-Obama, anti-Democratic rhetoric is not enough to fully validate their conservative credentials.

Since the 1950s, American conservatism has been defined by the writings of William F. Buckley, Jr. He and his editors of the magazine he founded, The National Review, defined the boundaries of conservatism to exclude people, ideas, and groups they considered unworthy of the conservative title. He denounced (atheist) Ayn Rand, the John Birch Society, George Wallace, racists, white supremacists, and anti-Semites. Buckley’s conservatism also was driven by his strong anticommunism.

The conservative values that Buckley stood for—unalienable rights, smaller government, lower taxes, strict interpretation of the Constitution, and so on—are the mantra of today’s conservatives, if not always their creed. Buckley understood that there would be those that deeply and uncompromisingly believed in them and those that were less committed. He differentiated between "conservatives" and “Conservatives,” Take for example Buckley’s perspectives on presidents George W. Bush and Ronald Reagan.

Of President George W. Bush, Buckley said, "Bush is 'conservative', but he is not a 'Conservative,' and that the president was not elected 'as a vessel of the conservative faith.'"

President Reagan, Buckley believed, embodied the heart and soul of American Conservatism. Reagan not only pursued conservative policies he deeply believed in and articulated clearly why he was a conservative and the fundamental conservative principles and values that Americans should aspire to. It is Ronald Reagan that every politician that covets the conservative mantle since seeks to identify with.

How, then, do the current conservative presidential candidates stack up against Ronald Reagan and William F. Buckley, Jr. They understood that it is not enough to simply say you are a conservative, to espouse popular conservative policies, or to be staunchly anti-liberal. You must intellectually know and effectively articulate why you are a conservative, instinctively possess deep seated conservative convictions, and consistently live by them.

Partisan rhetoric aside, American liberalism and conservatism have much common ground on which they can agree. Patriotic liberals and conservatives love America. They believe in and have fought and died for due process, equality under the law, the freedom of speech, the press, and religion. It isn’t necessary for liberals and conservatives to engage in incessant mortal political combat on all issues. They can agree on numerous policies and programs to solve America’s urgent problems.

At their core, however, the difference that divides them is that contemporary American liberalism seeks to control human nature, granting more power to “enlightened” elites and bigger government. American Conservatism—Bill Buckley’s and Ronald Reagan’s conservatism—wants to unleash human nature, channeling it for positive purposes and defusing power, to the maximum extent practical, to individuals and communities.

Herein we find the distinguishing mark of the true American conservative. On this fundamental conservative principle, there is little room for compromise.

The next time you listen to a candidate that says he or she is a true conservative ask yourself how confident you are that they will always err on the side of this most basic conservative value. Do their past actions and statements clearly demonstrate their faith and confidence in the American people to do the right thing when they have visionary conservative leaders like Ronald Reagan? Or do they lack that faith and confidence, erring on the side of government? This is not a difficult standard to apply. Granted, perfect scores are rare, but Reagan came close.

When it comes to voting in the 2012 election, however, you may find it necessary to follow Bill Buckley’s advice to “vote for the most conservative candidate that can win.” But do so with your eyes wide open.