As a rule, Republican candidates don't run against Fox.

For two decades, Roger Ailes' cable news network has been one of the most powerful conduits between GOP hopefuls and conservative voters. Nearly every Republican candidate has courted the network in some way or another, and some have even seen their presidential hopes rise or fall with the network's coverage of their campaigns.

So what happens if Donald Trump — the man who waged war against Fox News, insulted its star moderator and skipped its debate -- ends up winning the Iowa caucuses and goes on to win New Hampshire, the party's nomination, even the presidency?

That is a question that looms over Fox News as voters head to caucus sites here in the Hawkeye State. Should Trump net a win here just four days after defiantly skipping Fox News' debate, some political observers say it could send a signal to future insurgents that you can run a successful campaign by going around, or even against, Fox.

Related: Bill O'Reilly and Megyn Kelly's rivalry felt in halls of Fox News

"If Donald Trump wins this thing, it shows that you can do this without them," Bill Bennett, the veteran conservative pundit who recently criticized Fox News for its public statements about Trump, told CNNMoney.

"Historically, you have to go through Fox News," Bennett said. "They will still have influence over Republican primaries, but they will have hurt themselves."

No one believes that a Trump victory would deal a catastrophic blow to Fox News' viewership. Fox is the most-watched news network on cable, and it is likely to maintain its influence among Republicans (and others) for some time.

Related: Fox says Donald Trump is not telling the truth about its debate ad rates

But a Trump victory would show for the first time that it was possible to publicly oppose the network and still run a winning campaign. It might also reinforce the growing belief among far-right, pro-Trump conservatives that the network does not reflect their worldview.

Trump has already shown that a broad group of conservatives will side with him over Fox News. His attacks on Fox anchor Megyn Kelly and many of the network's contributors have done nothing to staunch his growth in state and national polls.

And when Trump skipped Thursday night's debate, ratings dropped to just half the total viewership of the previous Fox News debate in August. (Though far fewer people watched Trump's rally, which took place at the same time as the debate and was covered by rival networks, including CNN.)

Some of this is due to Trump's star power, of course. The real estate mogul and former reality television star is a singular figure in American pop culture. He commands the kind of ratings and national media attention that most typical candidates could only dream of. So in that regard, he may be more of an aberration than a harbinger.

Related: GOP candidates take cue from Donald Trump's anti-Fox playbook

"Donald Trump can get away with that, but I'm not sure many others can," said David Yepsen, who spent 34 years covering politics for the Des Moines Register. "He didn't need Fox to climb up the ladder, so I don't know that anybody else could replicate that."

It's also important to remember that Trump's rise has been fueled in large part by Fox News, despite their disagreements. Trump was a regular guest on Fox News prior to his presidential bid, and an even more frequent guest on the network during his campaign. Even when the Trump-Fox war was at a fever pitch late last week, Trump could still be seen on Fox airwaves giving a one-on-one interview to Bill O'Reilly.

Whatever the case may be, Trump has cast himself as the antagonist to Fox News, and he has convinced many conservatives to side with him over and against Fox News.

Already, other candidates are seeking to capitalize on that divide. At the Fox News GOP debate on Thursday, Sen. Ted Cruz mocked moderator Chris Wallace for his questions and even jokingly threatened to leave the stage -- the kind of anti-media attack Cruz regularly lobs against mainstream media outlets, but rarely against Fox News.

That clearly resonates with some conservatives here in Iowa. Outside a Ted Cruz rally in Davenport on Sunday, one supporters was heard telling others: "Fox News isn't the opposition, but they manage the opposition" -- a statement she said reflected her belief that the network was firmly aligned with establishment interests.