Cold war between 2016 GOP rivals Bush and Rubio heating up [...] that has eroded as the Florida Republicans battling for the presidential nomination have come to see the other as the main threat to lofty ambitions: The rise of GOP outsiders such as Donald Trump and Ben Carson has increased the stakes for Bush and Rubio as they try to become the mainstream alternative. Whoever wins this internal contest will show whether experience or fresh leadership is the bigger priority for GOP centrists. From Bush, there's a sense of urgency in his contention that Rubio, in his first Senate term, has not proved his leadership credentials. Evidence of the tension between the Florida politicians was on display Thursday when Rubio's campaign, minutes after the Bush organization announced raising $13.4 million in the last quarter, boasted it had more cash on hand. [...] about $1 million of Rubio's cash cannot be accessed unless he wins the GOP nomination, a point Bush campaign spokesman Tim Miller pounced on via Twitter. In New Hampshire recently, Rubio said the election is "a generational choice" and political leaders in both parties are "out of touch."