When Rick Santorum ran for the Republican presidential nomination in 2012, he won 11 states and nearly 4 million votes.

This time around, the former Pennsylvania senator never seriously threatened to have an impact on the race. CNN is now reporting that Santorum will end his campaign after receiving just 1 percent of the vote in Iowa — a state he won in 2012.

Santorum won 11 states in 2012, but sometimes struggled to get 11 people to his rallies this time around

In ending his candidacy, Santorum is really just acknowledging what has been clear for months: His path to the nomination has long since been crowded out by other, better-known alternatives.

Santorum’s first big challenge came in May 2015 when former Arkansas Gov. Mike Huckabee, who sat out the race in 2012, announced his presidential bid.

Huckabee has longstanding ties to the same social conservatives and evangelicals who had been crucial in powering Santorum’s 2012 campaign, and his candidacy shrank Santorum’s potential base of support.

But Santorum can’t blame his failed candidacy on Huckabee alone. Both Huckabee and Santorum would later be overtaken by Dr. Ben Carson, whose appeal to evangelicals was central to his polling surge. And Carson would himself be overtaken by Sen. Ted Cruz, who also drew the voters Santorum needed to be viable.

With his former supporters going elsewhere, Santorum struggled to remain relevant.

He was relegated to the "undercard" debate. His former Pennsylvania donors declined to open their wallets. Staffers began defecting to other campaigns. Santorum came in 11th of 11 candidates in RealClearPolitics’ polling average.

The press coverage became at turns mocking and pitying. The man who had posed the most serious challenge to Mitt Romney in 2012 sometimes failed to draw more than a handful of people to his events.

"Santorum calls crowd of 4 in rural Iowa a success," ran a headline in the Des Moines Register. Ouch.

Santorum fell victim to the coverage-polling cycle of doom

On the one hand, Santorum’s fall is an unremarkable example of politics as usual: Sometimes politicians who have strong credentials fall from the conversation, get labeled as unpopular, and never recover.

Vox’s Matt Yglesias explained how this dynamic works when looking at the (similarly underwhelming) candidacy of former Maryland Gov. Martin O’Malley, who on paper also seemed to have a plausible case for his candidacy.

Like O’Malley, Santorum didn’t poll well when the race began. That led the media to ignore his candidacy, which in turn sank his standing in the polls, which in turn justified even less press coverage.

This is the same basic problem that Theodore White identified in his book The Making of the President 1964:

The development of an image is a mysterious thing: once a public figure has been cast in a public role, it is almost impossible for him to change the character. It is as if someone has assembled personality traits into a convenient pattern, no writer ever re-examines it: it is easier to use the accepted pattern.

It’s as close as you can get to a general rule in politics: Once a candidate is considered a bit player, the image becomes almost impossible to shake.

The big new variable in 2016: the angry electorate

But if Santorum’s campaign fits a decades-old pattern of American politics, his failure also at least appears to reflect something that was genuinely different about this year — especially on the Republican side.

That difference is anger.

America’s bitterness toward the political system has been well-documented in poll after poll after poll. The New York Times’s David Leonhardt suggested that anger is the crucial difference between this presidential election cycle and all others in the modern era.

"Half of all Americans are angrier today than they were a year ago," Esquire wrote in a summary on "rage" in this year’s election. "White Americans are the angriest of all."

Why couldn’t Santorum channel the 2016 electorate’s anger?

Santorum was a poor vessel for channeling this widespread fury toward the political class.

That’s not really because of the substance of his campaign. Santorum has called deportations "a gift" for undocumented immigrants, made deeply homophobic remarks, and even declared that World War III is already underway.

The real challenge was his style — his ho-hum stump speeches and genial appearance, which National Review’s Tim Alberta memorably described as "a breathing facsimile of Woody from Toy Story."

Compounding the difficulty of a credibly anti-establishment message was Santorum’s record, which includes more than a decade in the US Senate, a stint as chair of the Senate Republican Conference, and connections to K Street lobbyists.

For his part, Santorum appears to have understood the gap between the passion he could convey what the voters wanted to see.

"There’s a difference between fighting and anger," he told a Tea Party rally in January, according to Breitbart News. "Please pray and do the right thing. Don’t act out of anger."

The one quote that shows why Santorum was such a bad fit for 2016

There are lots of examples to illustrate Santorum’s anger gap, but I think a Politico story by Kyle Cheney from this fall provides a particularly useful (if inadvertent) illustration of Santorum's problem.

It starts in 2011, when Donald Trump (who else?) called Santorum "a loser" while on Fox News.

After seeing the clip, Santorum called Trump in what seems to have been an earnest attempt to point out that Santorum did not agree that he was, in fact, a loser.

Here’s Politico:

Santorum, a former Pennsylvania senator who lost his reelection campaign in 2006, said he happened to catch Trump's insult while watching TV. Their phone call, though, was a largely cordial conversation, with Santorum framing his Senate race defeat as a business deal gone bad.

The story then moves ahead to 2014, when Trump staffers mistakenly accused Santorum of denigrating the real estate mogul during a radio interview.

Afterward, Santorum met with Trump in New York City:

They had an hourlong conversation "about everything (Trump) was doing" — including his deal to convert the Old Post Office in Washington, D.C., into a luxury hotel, which Trump insisted has infuriated President Barack Obama. "An hourlong conversation, I probably talked about 10 minutes," Santorum said.

Santorum seems to try to use the anecdote to reveal his reasonableness and maturity, especially compared with the brash real estate mogul.

But it also reveals something else: that Santorum could simply be talked over, and drowned out, by the louder voices in the room.