Mr. Summers had long been viewed by Mr. Obama and his economic advisers as Mr. Bernanke’s presumptive replacement

After weeks of opposition to his candidacy from an array of progressives, the president’s inability to rally Congressional Democrats on Syria persuaded Mr. Summers that his most important audience — the Senate, which must confirm a Fed chairman — probably could not be won over.

He concluded that the White House was also unlikely to overcome opposition to his candidacy from many of the same Democrats, who view him as an opponent of stronger financial regulation, according to supporters who insisted on anonymity to describe confidential conversations with him.

“Clearly Obama couldn’t bring his own most enthusiastic supporters to back him on an issue of national security,” one supporter said. “How was he going to corral them for Larry?”

Bloomberg: Senator Warren's 'Serious Concerns' About Larry Summers

Senator Elizabeth Warren has told the White House that she won't publicly take a position on Larry Summers as a possible chairman of the Federal Reserve Board, though she privately told administration officials she has "serious concerns" about him as a nominee, according to people familiar with the situation.

Summers's prospects have dimmed over the past week and the Obama administration has come to realize the opposition of a prominent figure such as Warren could deliver a fatal blow, several people said.

...

That might be a miscalculation. Yesterday, Senator John Cornyn of Texas, the second-ranking Republican in the Senate, told the Huffington Post that he would oppose a Summers nomination. Although some economists say Yellen would be a little more liberal on regulation and monetary policy, Summers, with his close involvement in Democratic politics and policies over the past two decades, would raise more suspicion among the Republican Party's right wing base.

White House officials privately have predicted Summers would win Senate confirmation because even if a handful of Democrats defected, the nominee would have sufficient Republican supporters, who would be swayed by financial interests that would back Summers.

"One of them, Michele Ferri, told CBS News about a recent conversation. Ferri wrote a letter to the Pope in a moment of rage; but was shocked when she picked up the phone and heard:"'Hi Michele, this is Pope Francis.'"

I never imagined that the Pope would call me on my cell phone," said Ferri. "I thought I would get a form letter perhaps. But never a phone call."

Reportedly, the Pope called a divorced pregnant woman and offered to baptized her baby; she wrote to the pontiff when her boyfriend pressured her to have an abortion. There were also reports that Francis also responded to a rape survivor's letter.