If the debate in South Carolina two weeks ago represented the Republican primary in microcosm, this one was like a randomized controlled trial: What would the GOP primary look like without Donald Trump?

True, Trump’s absence was hard to ignore during the first 30 minutes of the debate. It didn’t help that the Fox News moderators focused their first few questions around Trump. The other candidates seemed a little unsure of themselves.

But by the second half of the debate, you had — as Chris Wallace reminded Ted Cruz — an actual debate. It was a good and vigorous discussion, with lots of tough questions posed by Wallace and Megyn Kelly. And it gave us a glimpse of which candidates are most diminished by Trump, and which seem to benefit from his presence.

According to our staff grades, the candidate with the best night was someone who’s usually forgotten about … Rand Paul. With his libertarian-leaning views, Paul is a hard guy for the media to characterize: He’s certainly not an “establishment” candidate, but he also doesn’t fit the stereotype of a fire-breathing, red-meat conservative. In an election without Trump, Paul might be among the more interesting candidates for the press to cover. In an election with Trump, he’s treated as an afterthought.

FiveThirtyEight’s Republican debate grades CANDIDATE AVERAGE GRADE HIGH GRADE LOW GRADE Rand Paul B A C Marco Rubio B- A- C Jeb Bush B- A- D Chris Christie B- B+ D Ted Cruz C+ B+ D John Kasich C+ B D Ben Carson D+ B F

The bar is pretty low, but Jeb Bush also had one of his better performances, receiving a B- grade. It’s hard to know how much of Bush’s disappointing campaign can be blamed on Trump: Many of his problems were apparent from the start. But every candidate has problems, and Bush isn’t fundamentally all that different from Mitt Romney, who won the nomination four years ago. Trump seems to have a particular talent for drawing out Bush’s least appealing qualities, while Bush appeared more self-possessed without Trump on stage.

By contrast, our group thought that Ted Cruz had his worst performance of the cycle, giving him a C+. Without his frenemy Trump on stage, Cruz had two problems: First, as the highest-polling candidate at the debate, he was more of a lightning rod for attacks. Second, without the histrionic Trump as a comparison, Cruz’s delivery showed its rough edges, at times being both corny and sanctimonious. More importantly, Cruz’s strategy of positioning himself as the “compromise” between Trump and the more conventional candidates no longer looks so brilliant anyway, as Republican leaders have turned on him.

Marco Rubio’s performance didn’t seem to be affected much one way or the other by Trump’s absence. That seems to be true of Rubio in general, actually: He isn’t affected all that much by the context, polling about equally well with every demographic group in every state. Unfortunately for Rubio, that’s not good enough to win him any states, although there are signs of forward movement for him in Iowa.

Still, I find it pretty hard to guess how Republican voters will react to all of Thursday night’s action. Take Rubio, for instance: I thought that he was pretty solid overall but that he got roughed up by Kelly on immigration. How will voters weigh those two things? Both the pundit reaction and the Fox News focus group were more sympathetic to Rubio than I would have guessed, but neither of those are the most reliable benchmarks.

Instead, we’re in the “fog of war” phase of the campaign. It’s hard for reporters, including us at FiveThirtyEight, to judge what the debate looks and sounds like to voters at home who aren’t as immersed in the campaign and who haven’t heard the same catchphrases delivered so many times. Moreover, it’s not just any Republican voters but a very narrow subset of them who matter right now — the perhaps 125,000 or 150,000 Iowans who will caucus Monday, maybe one-third of whom are undecided or could still plausibly be persuaded to change their minds. That’s somewhere in the neighborhood of 30,000 to 50,000 people who will go a long way toward determining the Republican Party’s future. And I wouldn’t put a great deal of trust in us or any other journalists’ guesses about what they might be thinking.

For that matter, while it was predictable that many reporters couldn’t resist the storyline that Trump won the debate by not showing up for it, I’m not sure that’s so obvious either. I understand the case: Trump’s leading rivals didn’t have a great night, and Trump continued to command the lion’s share of attention despite not being on stage. But Trump pretty much always dominates the media conversation; that’s priced into the polls already, and we’ll still have to see how well he closes the sale with Iowa voters. For the next four days, the impressions of those 50,000 or so persuadable Iowans are all that matters.