The first, best hope of the anti-Hagelians was a bipartisan split. They wanted a Democrat worried about re-election, or worried about alienating donors, to be so worried about Chuck Hagel that he came out against the nomination. The story would have become "Nominee Under Fire From Both Parties." Alas, after a few teases—mostly Ben Cardin and Chuck Schumer declining to immediately endorse the nominee—they failed to get converts.
On to plan B: A Hagel filibuster. If Republicans can hold 41 of their 45 members and oppose Hagel, theoretically, they can block him. But there's very little precedent for that, and Democrats may already have 57 votes. The last Cabinet nominee who straight-up lost a Senate vote was John Tower, facially easy to compare to Hagel because he, too, had been a senator, and he, too, was up for Defense. While Hagel's being challenged on comments about Israel and Iran, Tower was sunk by stories about his drinking and womanizing. He took revenge for the rest of his life, comparing the Senate unfavorably to Beirut, where murderers at least have the decency to "hurl a grenade at someone or shoot a machine gun."
But Tower was a Republican nominee rejected, with 53 "no" votes, by a Democratic Senate. Since 1975, when the margin for a filibuster was set at 60 votes, no Cabinet nominee has ever been subjected to it.
"I don't think he's going to lose any Democratic votes, that we know of," Sen. Carl Levin told reporters after the hearing. "I think there's at least a few Republicans who've already said, publicly, that they support his nomination." When pushed, he could barely name two. "What I've heard—I've heard that Sen. Cochran, and I've heard Sen. Murkowski. That's third hand. If nobody in this crew has heard that Sen. Murkowski is inclined, then I will withdraw that comment."
He didn't brim with confidence, but that's not really the Levin style. And you don't pound your chest if your only impediment is an unprecedented filibuster.