If it wasn't clear before, it is now: Things are nasty between Sens. Marco Rubio and Ted Cruz.

Rubio's campaign released a memo Sunday afternoon accusing Cruz of "running the nastiest campaign South Carolina has ever seen." The Texas senator would "truly say anything at all to get elected," Rubio's release says.

"In South Carolina, Sen. Cruz continued his campaign of lies, falsehoods, and underhanded tactics that first began in Iowa with false rumors about Ben Carson," Rubio's campaign wrote. Rubio was referring to a false rumor the Cruz campaign spread about Ben Carson supposedly dropping out of the race after the Iowa caucuses.

Rubio said little about Donald Trump, the only candidate who beat him on Saturday, other than to note Trump's high negative ratings and to propose that the race for Republican presidential nomination is now a "three-man race" between himself, Trump and Cruz. Rubio's refusal to hit Trump hard appears to be part of a deliberate strategy, but one that has baffled of the senator's supporters.

Rubio's focus on Cruz instead of Trump could be attributed to more overlap in the voting base between the two senators. And as other candidates drop out of the contest, their voters are more likely to move to Rubio or Cruz rather than towards Trump.

"Just in the past week, we saw the Cruz campaign and their allies unleash a wave of lies about Marco's record, false rumors that Marco was dropping out, anonymous push polls, outrageous robocalls in both English and Spanish, fake Facebook posts, personal insults directed at popular South Carolina leaders, and ads that had to actually be taken down," the memo said.

Rubio and Cruz in particular have competed for evangelical voters. Cruz tried hard to court them ahead of the South Carolina primary, but fell dismally short there without winning in any single county and ultimately coming in third place. The Rubio campaign boasted that it took a "significant part" of the evangelical vote and said Cruz came in far short of expectations.

"If Ted Cruz can do no better than third place in a state like South Carolina where 73 percent of the electorate described themselves as "born-again or evangelical Christian," where else can he win?," the Rubio memo said.

Rubio took a similar to tone to Trump, who has also accused Cruz of lying in order to get ahead in the race. Trump even sent Cruz a cease-and-desist letter last week warning him to take down ads Trump called misleading. Rubio's memo said Cruz would "say anything" to gain a foothold in the election — and predicted that would be a turn-off to voters.

"As we saw in South Carolina, Sen. Cruz's willingness to say or do anything in order to win an election does not wear well on voters," the memo said.