The rallying cry hashtag: #PrimaryGraham. | John Shinkle/POLITICO Graham's very bad day on Twitter

As good a day as this was for Sen. Rand Paul on Twitter, it was at least that bad for Sen. Lindsey Graham.

Laced throughout the thousands of tweets cheering on the filbustering Kentucky Republican was a vicious, visceral anger aimed squarely at the South Carolinian up for reelection next year.


The rallying cry hashtag: #PrimaryGraham.

( WATCH: Rand Paul responds to McCain, Graham criticism)

“This very well could be a defining moment in this particular campaign — the moment Lindsey Graham lost his grip on the boots on the ground in South Carolina,” Daniel Encarnacion, state secretary for the Republican Liberty Caucus, said in an interview.

Paul emerged as a folk hero whose appeal spread far beyond his tea party base for perhaps the first time, as seen by the enduring strength of the hashtag #StandWithRand. More than 18 hours after Paul yielded the floor following a 13-hour stemwinder, it continued to trend.

One reason for that longevity: Graham and Sen. John McCain (R-Ariz.) took to the Senate floor to castigate Paul and express disappointment in fellow Republicans such as Minority Leader Mitch McConnell and Texas Sen. Ted Cruz for supporting the filibuster.

The episode was already not looking great for Graham before he rebutted Paul on Thursday. Graham and McCain were dining at the White House with Obama while Paul was filibustering, a contrast picked up early and often by many online.

“Not only is @LindseyGrahamSC missing from tonight he has openly mocked” the filibuster, groused Randan Marie Swindler, a former staffer to Sen. Jim DeMint (R-S.C.). Then came two hashtags: #StandWithRand and #PrimaryGraham.

Graham’s decision to vote for John Brennan as CIA director — a response, he said, to the Paul filibuster — further infuriated his many Twitter critics.

Graham did not respond to requests for comment.

The senator was already looking like a primary target for his conciliatory gestures toward Democrats on immigration and sequestration. Missing, however, had been a certain level of outrage — anger that is now exploding on social media.

“The way he responded to it today on the floor was particularly a setback for him within the grass-roots movement,” Encarnacion said. “People who have given him the benefit of the doubt within the regular GOP ranks here are no longer giving him the benefit of the doubt.”

One name that surfaces regularly as a likely primary challenger is state Sen. Lee Bright of Spartanburg. His name was floated again by callers on Glenn Beck’s radio show Thursday, and although he’s undeclared, sources say he already has a campaign manager in place.

What may be holding him back is money. Graham has a war chest in excess of $6 million, which South Carolina-based GOP digital strategist Wesley Donehue said “goes a long way in our cheap media markets.” Donehue doubts the anti-Graham flare-up over Paul’s filibuster will last long because “there is no one for the pissed-off Internet crowd to give money to.”

( PHOTOS: Highlights from Rand Paul’s filibuster)

People like Encarnacion believe that could change pretty quickly if, say, Paul were to swoop in to do a fundraiser or campaign for a Graham alternative. Paul, of course, was himself an outsider who beat establishment candidates in Kentucky en route to his seat.

“No doubt the money Lindsey Graham has is a significant roadblock for challengers to go after him, but we have seen time and time again where grass-roots activism and the passion people have overcomes that,” Encarnacion said. “What I saw yesterday and what I’m seeing today is that people identify with what Rand Paul said yesterday. Yesterday, we were all Rand Paul Republicans. And then Lindsey Graham jumps all over that.”