I'll be honest: The prospect of Hillary Clinton winning her party's nomination without even trying and then coasting to victory in the general election against a lame Republican opponent leaves me feeling depressed, and not only because I'm paid to write about politics.

Our political system ought to do better than that — by giving the American people a genuine choice. But most of the likely matchups wouldn't do that.

Clinton is a centrist Democrat all the way down. She's spent the past 22 years near the peak of power inside the Beltway. If she ends up squaring off against Paul Ryan, Marco Rubio, Chris Christie, Jeb Bush, or (God help us) Mitt Romney, it will be a contest played out from deep within the reigning Washington consensus.

The candidates will pretend to disagree about foreign policy, but it will be an act, with neocon-ish Clinton perfectly matching her opponent's blustery bellicosity point for point.

On domestic policy, Clinton will promise to defend ObamaCare while reforming its least popular and least successful elements. She'll also signal her intent to do what Democrats always do, which is to protect government programs and keep tax rates at their current level or raise them slightly on the top end.

The Republican, meanwhile, will do what Republicans always do, which is to rail against government and promise tax and spending cuts that everyone knows will translate into tax cuts for the wealthy alone, sending the deficit back into the stratosphere. (Despite what Republicans say in their speeches, their actions reveal that it is not the deficit that matters to them, but rather cutting taxes on the highest earners while protecting government programs that benefit the aging white voters who form the base of their party.)

There is only one realistic way to break out of this tired state of affairs. And no, it doesn't involve a run by Ted Cruz, Rick Santorum, or any other candidate from the GOP's delusional there-are-more-general-election-votes-on-the-far-right-than-in-the-center caucus. If someone from that faction manages to land the nomination, I fully expect the median-voter theorem to be vindicated and Clinton to win in a historic landslide.

No, the only scenario that promises to deliver a genuine contest and spark a serious, important debate is one that involves an electoral smackdown between Clinton and Rand Paul. That is the presidential matchup America needs.

Let me be clear: I am not a libertarian. It's very unlikely I will cast a vote for Paul or any other Republican in 2016. I anticipate supporting Clinton in the general election.

But I nonetheless believe that American democracy would benefit from a contest that forces the establishment candidate (Clinton) to defend herself and her positions against a challenger who presents a genuine alternative — and one who confounds at least some of the pieties that have gripped the GOP through the last several election cycles.

The biggest contrast would be felt on foreign policy. Paul's expressions of support for a military response to ISIS have obscured just how skeptical he is of the GOP's reflexive, unmodulated hawkishness, which inspires nearly all of its leading figures — as well as a good many Democrats, very much including Hillary Clinton — to propose military force as an all-purpose solution to nearly every problem in the world. Paul appears eager to break from this consensus in favor of a stricter calculation of America's national interests, and with those interests defined more narrowly than neocons and liberal interventionists tend to do.

Paul's desire to reorient America's foreign policy extends to other aspects of the national security state that has emerged in the U.S. since the terrorist attacks of Sept. 11, 2001. As Americans learned from his blockbuster 13-hour filibuster on March 6, 2013, Paul strongly opposes warrantless surveillance and extrajudicial killings, especially when American citizens are targeted. Clinton's position on these issues, by contrast, is...somewhat more difficult to pin down.

Paul's libertarian suspicion of government police powers even led him to criticize the Ferguson, Mo., police department in the wake of the shooting death of the unarmed 18-year-old Michael Brown. In a column for Time, Paul declared that "it is impossible for African-Americans not to feel like their government is particularly targeting them." That might sound like an uncontroversial position, but for a member of a party that has defined itself since the era of Richard Nixon as a champion of law and order and unapologetically tough on crime, it is.

When it comes to taxes and entitlements, Paul is closer to being a mainstream Republican — though his libertarian commitments give us reason to think he may be slightly more willing than other members of his party to match tax cuts with real reductions in spending. I don't support slashing either taxes or spending, but if we're going to have the first, it's far better to combine it with the second than to pay for the tax cuts by increasing levels of public debt.

Now, none of this means that Paul will have an easy time on the campaign trail. On the contrary, as Ross Douthat argued last spring, Paul will likely face long odds in the primaries precisely because his agenda simultaneously challenges so many elements of the GOP electoral coalition.

And even if he does somehow run the Republican gauntlet and manage to come out at the head of the pack, he'd still have to face the Hillary Clinton juggernaut in the general election. Despite recent hype about a "libertarian moment," I tend to think Clinton would do quite well in such a matchup.

But I could be wrong. And wouldn't it be clarifying to test the proposition?