WASHINGTON (Reuters) - Donors say Republican Jeb Bush’s U.S. presidential campaign has not given them a green light to switch to rival establishment candidate Marco Rubio, whose strong third-place finish in this week’s Iowa caucuses outshone the sixth-place Bush.   A former Florida governor, Bush, 62, is hoping for a better result in New Hampshire, the state which on Tuesday will hold the country’s second nominating contest for the Nov. 8 election to succeed President Barack Obama. U.S. Senator Rubio, 44, also of Florida, emerged as the leading moderate, establishment Republican candidate in Iowa, behind U.S. Senator Ted Cruz of Texas, 45, and billionaire businessman Donald Trump, 69.  Senior campaign officials for Bush have been seeking to reassure donors that the one-time front-runner has a path forward after his dismal Iowa showing, three Bush donors told Reuters. They said senior aides to Bush held conference calls for donors on Tuesday to reassure them, offering an upbeat message about Bush’s finances and ground game in New Hampshire and a determination to press on.     Rubio began the year with more than $10 million in cash on hand, his campaign reported on Sunday. Bush reported cash on hand as of Sunday of $7.6 million. Bush, campaigning later this week in New Hampshire with his mother, former first lady Barbara Bush, has benefited from the intense loyalty donors have shown his father and brother, former presidents George H.W. Bush and George W. Bush. The donors said there was no indication Bush would shy away from contrasting himself with either Rubio or Cruz.     “People who are for Jeb are for Jeb,” one donor said. On the campaign trail this week Bush has questioned the abilities of freshman U.S. senators - both Rubio and Cruz are first-term senators - by saying they lacked his proven record.  (Reporting by Steve Holland; Editing by Howard Goller) SAP is the sponsor of this content. It was independently created by Reuters’ editorial staff and funded in part by SAP, which otherwise has no role in this coverage.