Senate Majority Leader Harry Reid (D-Nev.) will have to find 60 votes to extend just the middle-income tax rates — far from a given when a swath of the Senate’s moderate Democrats are up for reelection in 2014.

Reid and the White House will also need to navigate a hardening Democratic divide on entitlements. Progressives don’t want any deep cuts that Republicans will insist on for a deal. But a Third Way poll of 800 Obama voters set for release Tuesday found that efforts to fix Medicare and Social Security enjoy broader support than liberals suggest.

Even if Speaker John Boehner (R-Ohio) were to risk his job by backing a tax-rate increase, there are Democrats who think a $250,000 income threshold is too low. So finding 218 House members to pass a bill that would extend the lower tax brackets isn’t exactly a cakewalk. Want Boehner to raise taxes? Republicans privately say the entitlement changes would have to be unimaginably sweeping.

In a nutshell, Democrats haven’t yet coalesced around a position themselves, let alone found agreement with Republicans.