The two hottest conservatives in the Senate came to CPAC on Thursday showing their respective strengths. Sens. Rand Paul (R-Ky.) and Marco Rubio (R-Fla.) appeared back to back, maybe a preview of a heavyweight fight in 2016.

Sen. Marco Rubio at CPAC-JIM LO SCALZO/EPA

Rubio was focused on the world around us and the problems conservatives can help fix. He looks at the globalized world and sees change and challenges. He tells us we can’t check out of the world but must engage economically and not leave world leadership to countries like dictatorial Communist China. Yes, he’s an internationalist, but it is internationalism grounded in American values and self-interest. In making the case for international involvement, he tied it directly to creating middle-class jobs.

He spoke directly about the middle class, about “applying our time-tested principles to the challenges of today.” Rather than take up the cause of spending cuts, he focused on economic growth, educational choice, the breakdown of the family and conservative health-care reform. He stressed (as other conservatives, such as Rep. Paul Ryan and Sen. Mike Lee, have lately) community associations and civic institutions. In charming fashion he talked about a modest-income family he knew through his 7 year-old son’s football team (“They’re not freeloaders. They’re not liberals”) whom the conservative agenda should appeal. He explained how what he is offering can make a difference in that family’s life.

Rubio didn’t touch on immigration, but it was bold and cheery speech, rebuffing the suggestion that Americans have become too dependent and lazy (no 47 percent speech for him). He got big applause for the line “We don’t need new ideas. The idea is America and it still works”; yet his speech was, in fact, about new applications and insights into policy. He sounded like a traditionalist on values, but in fact his formulation was perfectly in sync with gay marriage decided on a state-by-state basis (“just because I believe that states should have the right to define marriage in a traditional way does not make me a bigot”).

Rand Paul’s speech was almost entirely theoretical. It was an ode to freedom, to defending individual rights and to not losing our civil liberties in fighting our enemies. He demands that President Obama not take away our right to a jury or “drone us.” His tone is defiant. (“Mr. President, will you or won’t you defend the Constitution?”)

He was light on policy. He wants to cut the corporate income tax in half and have a flat tax while balancing the budget in five years. Other than that, he is focused on making sure the executive and judicial branches remain separate, that government get off our backs and that we limit government so liberty can expand. The mostly college-age, white crowd ate it up. He said he wants to sell his message everywhere in America, but is that a message that is going to capture the imagination of the modest-income family Rubio described?

While Paul sounds newer than many Republicans because his message is more libertarian and distinctive (he mentioned drug legalization but not same-sex marriage), the risk is that he appeals only to the very same people who are already Republican or libertarian. Health care and education? That is where government stops acting; what happens next is left unsaid. In the 21st century his world view expresses a nostalgic desire to be left alone and to wash our hands of messy conflicts. But is that the world in which we live and can we thrive economically without a stable and mostly free planet?

Both senators are funny and natural speakers. Both are colorful in language and culturally attuned. Both want government to tax less and spend less. But these are very different men with very different worldviews. Paul harkens back to a pre-New Deal government; Rubio wants to modernize the government we have. Paul is there to protect us against the government; Rubio is there to make it constructive.

Which way does the GOP go? That, in large part, depends on how these two figures mature and what success they have in persuading fellow conservatives of the relevance of their message. Now they complement each other, but at some point they will have to directly engage.

It strikes me as a debate that is hugely productive for conservatives, the end product of which will be a 21st brand of conservatism that can not only hold up to intellectual scrutiny but can also lead the GOP to victory at the presidential level and back into a majority in the Senate.