As Marco Rubio has risen in the polls following quality debate performances, Jeb Bush has continued to slowly drop out of the top tier, also on the merit of his debate performances. At this point in the race, both candidates are vying for the same chunk of support among Republican voters and the big-money donors who often prop up and support the establishment favorite.

Report from ABC News:

As is always the case in politics, there are friends and foes, allies turned archrivals.

But for GOP candidates Jeb Bush and Marco Rubio, the relationship is far more nebulous. The longtime mentor and protégée are now seeing themselves forced into a rivalry by a primary that, whether they like it or not, has pitted the two Floridians against each other.

And while they still attempt to remain civil, the long-brewing battle between the two camps is slowly bubbling up.

Bush’s son, Jeb Jr., unleashed on the senator while speaking to a group of College Republicans in New York last week.

“As a Floridian, I’m a little disappointed, because he’s missing, like, 35 percent of his votes,” Jeb Bush Jr. said of the U.S. senator from Florida, according to Politico. “And it’s just, kind of, like, dude, you know, either drop out or do something. But we’re paying you to do something; it ain’t run for president.”

Rubio has missed 29 percent of Senate votes in the past year.

Jeb Bush Jr.’s words went much further than his father’s, who usually speaks in generalities about Rubio’s missed Senate votes, choosing instead to allude to his performance without invoking Rubio by name unless asked specifically.

When asked by reporters in New Hampshire about whether Rubio is shirking his responsibilities, Bush, 62, toed his oft-walked line of civility.

“I just think you have a responsibility to serve. And some of these votes actually matter, defense appropriations bills matter, committee hearings dealing with real challenges that our country faces. Marco’s got great ideas on these things, but he got elected to serve,” Bush said.

Rubio has been somewhat reluctant to fight back.

“When candidates are running, I think they’re going to say things that they think will make them stronger in the race. They’re going to attack people,” he told reporters who asked about Bush’s comments a few days later.

“I have great admiration and respect for [Bush] as a person. I’m not running against Jeb Bush. I’m running for president,” he added, reiterating the usual response he has given to questions about Bush since he first joined the race.

The relationship between Marco Rubio and Jeb Bush has become muddled with Bush’s unexpected drop in the polls and inability to gain traction following the first two debates. Rubio is looking like the alternative to the Donald Trump candidacy as GOP donors are seeking the establishment favorite who seems the most electable in the general election. That used to be Jeb Bush, but his lackluster debates have left his fundraising, once the strongest in the field, to a more reserved stream of support. So tough is Bush’s position that he’s begun taking shots are Rubio instead of Trump or Carson.

Rubio and Bush are fighting in the semi-final to earn a spot in the final and take on the “outsider” candidate that hangs on the longest. In this case, Trump continues to see strong poll numbers and until a few more of the “insider” candidates drop out, that support remains divided and neither Bush nor Rubio can go much higher. Thus, the current predicament which may begin to play out on the debate stage next Wednesday.