Kentucky Sen. Rand Paul and Arizona Sen. John McCain are once again banging heads – this time over whether to arm Syrian rebels – in the latest dispute that underscores a divide in the GOP and intensifies the fight over what the party will represent in 2016 and beyond.

Paul, a first-term senator and Tea Party favorite surging in popularity, took the latest shot by opposing aid to the rebels – a key part of McCain’s plan to end the two-year Syrian civil war in which 70,000 civilians and others have been killed.

“It is very clear that any attempt to aid the Syrian rebels would be complicated and dangerous, precisely because we don't know who these people are,” Paul wrote in an opinion piece earlier this week. “The situation in Syria is certainly dire. … Al Qaeda is making confirmed inroads into the country. No one wants to see Syria become a bastion of extremism. But like other American interventions in the past, U.S. involvement could actually help the extremists.”

But McCain, fresh off a secret trip to Syria, on Friday upped his call for intervention -- telling the Associated Press the opposition needs heavy weapons.

McCain and Paul split last month as members of the Senate Foreign Relations Committee when McCain, elected to Congress in 1983, voted in favor of the Syria Transition Act, which calls for “limited lethal and non-lethal assistance and training to vetted Syrian groups.”

Paul voted against the bill and warned in his op-ed Thursday for CNN that the U.S. now “has reason to believe” that Libyan rebels who helped overthrow dictator Moammar Gadhafi and whom McCain appeared to supported in 2011 were in fact connected to al Qaeda and other Islamic extremists. The bill passed by a 13-5 vote.

Their ideological fight is just one of several among Republicans as members seek to define and reshape the party after losing the last two presidential elections.

Party leaders are split over how to broaden their appeal to voters while maintaining such core values as small business growth with less government and taxes, especially after Hispanics, the county’s fastest growing population, last year gave President Obama roughly 71 percent of their vote.

Meanwhile, House Speaker John Boehner continues to struggle with a strong-minded conservative caucus for control of the chamber. Caucus members have not supported Boehner on several key issues including his own plan to keep the country from going over the so-called "fiscal cliff."

Boehner was forced in December to pull his bill from a floor vote at the last minute upon realizing he didn’t have the votes.

“What are you guys doing?” Rep. Mike Kelly, R-Pa., said afterward. “How the hell can you do this to the speaker?”

And now the country waits to see how much influence the Tea Party movement will have on Republicans after helping them win the House in 2010, backing a couple of flawed Senate candidates in 2012 and appearing to regain momentum after the revelations last month that groups were targeted by the IRS.

The disagreement over Syria and how to remove leader Bashar al-Assad, who has been accused of using chemical weapons on civilians, is just one disagreement between McCain, the 2008 Republican presidential nominee, and Paul, who appears to be considering a 2016 presidential run.

The 76-year-old McCain appears to have cut the divide between the older and newer Capitol Hill Republicans in March when he called Paul and newly elected Texas Sen. Ted Cruz “wacko birds” for their firebrand style of politics and their nearly 13-hour filibuster to demand Obama make clear his rulings for drone strikes on U.S. soil.

McCain apologized to Paul and Cruz, another Tea Party favorite with possible 2016 aspirations.

But the apology might have come too late for Paul, who already this year has made trips to the early voting states of Iowa and New Hampshire to address Republicans.

“The GOP has grown stale and moss covered,” Paul said at the 2013 Conservative Political Action Conference. “I don’t think we need to name any names, do we?”

A Quinnipiac University poll released Friday showed Paul with higher favorability rating than former Florida Gov. Jeb Bush, another potential 2016 Republican candidate.