Lindsey Graham has called it quits.

On Monday — not coincidentally, also the deadline for presidential candidates to remove their names from the South Carolina primary ballot — the hawkish Palmetto State senator, who has struggled to register in the polls and never once made the GOP's main debate stage, announced he was suspending his campaign.

I regret that I haven't been a better candidate. I regret that I never got on the big stage. I regret that I didn't make it to the final group. But that's just about me. I have no regrets about running for president. It has been the joy of my life to run for president of the United States. [Lindsey Graham]

Graham is right to have no regrets. He can go out with his head held high. Because while he didn't earn a lot of voter support, he earned the respect of Americans on all points of the political spectrum.

Graham won every "undercard" GOP presidential debate. He did so through his use of humor ("Lindsey Graham's one-liners stole the show during the Republican undercard debate," this very website crowed last week), and by virtue of his tremendous knowledge and passion for foreign affairs and national security. If the happy hour debates needed to be put out of their misery before Graham left, without him, all future undercard debates will be utterly unwatchable.

Indeed, as I noted the morning after the most recent GOP debate, nobody on the main stage made as compelling a defense of Bush-era hawkishness as did Graham during the "happy hour" debate. You might not agree with Graham's hawkish stances, but nobody in the establishment lane (including George W. Bush's own brother) has made the case for a robust foreign policy better than Graham has.

This actually highlights a big problem for the GOP: The party lacks a clear identity on foreign policy. The presidential candidates doing the best in the Republican race (think Donald Trump and Ted Cruz) are making what some might describe as "America First" arguments. Meanwhile, it's entirely possible that the Republican nominee for president might end up attacking Hillary Clinton from the left by calling her a "neocon." (Rand Paul is a longshot, I know, but that's his lane.) Are we in the midst of a great reordering, where Republicans return to a pre-World War II mindset of hunkered-down non-interventionism? Clearly, Graham fears this is the case.

There are many reasons why politicians who know they cannot win get into presidential races — some more noble than others. Some opportunistic candidates lamely and cynically hope to raise their status and land speaking gigs or a cable TV show. But others run because they have something to say, and nobody else is saying it.

Lindsey Graham was such a presidential candidate.

Graham clearly saw what he might call an isolationist (and others might call a non-interventionist) trend in the GOP, and he didn't like it. He ran to push back on this movement, and fight it intellectually.

In this regard, Graham succeeded. No one has made as convincing a case for a hawkish foreign policy in years.

Don't be surprised if by running for noble reasons, Graham doesn't also prosper personally. Some people wilt under the glare of the lights, but Graham rose to the occasion. It's easy to imagine him being secretary of defense in a Republican administration, more proof that sometimes you can do well by doing good.

But beyond his endearing zingers and genuinely held policy positions, Graham's greatest mark on the 2016 race may be this: He was the only candidate unafraid and honest enough to call Donald Trump what he is: a "race-baiting, xenophobic, religious bigot." Here's what Graham said to Trump's supporters during a CNN interview earlier this month:

I don't know who you are and I don't know why you like this guy. I think what you like about him, he appears to be strong and the rest of us are weak. He's a very successful businessman and he's gonna make everything great. He's gonna take all the problems of the world and put 'em in a box and make your life better. That's what he's selling.

Here's what you're buying: He's a race-baiting, xenophobic, religious bigot. He doesn't represent my party. He doesn't represent the values that the men and women who wear the uniform are fighting for... He's the ISIL man of the year. [Lindsey Graham]

Bravo, senator. The 2016 race will miss you.