It seems like just a few months ago a lot of pundits marveled at congressional Republicans’ lockstep unity and discipline in obstructing almost every legislative proposal introduced by Democrats, in stark contrast to earlier eras when Republicans would usually compromise for the good of the country. Republican still have the power to obstruct progressive legislation. But there are signs that GOP unity is beginning to unravel.
As Ronald Brownstein puts it in his National Journal post, “A Role Reversal: Dems Grow More Unified While Cracks Form in the GOP“:

The endgame over the fiscal cliff, like the first stirrings of debate about gun control and immigration, all capture a subtle but potentially consequential shift in the Washington dynamic.
On each front, Democrats are growing more unified while Republicans and conservatives are displaying increasing cracks. That inverts the alignment through most of President Obama’s first term–and indeed most of the past quarter-century.
In the decades immediately before and after World War II, both parties were divided in Congress between the moderate and the more ideological wings. But since the 1980s, the two sides have diverged. Conservatives have established unquestioned dominance in the GOP. Meanwhile, Democrats, though moving to the left overall, have maintained much greater divisions.
The debates over taxes, guns and immigration all reflect this evolution. Not long ago, each issue divided both parties.

Brownstein provides several instructive examples of political divisions within the two parties and temporary bipartisan agreements that emerged in congress during the Reagan, Bush and Clinton administrations. Brownstein then describes the beginnings of the transformation:

But while Democrats have remained divided on all three issues, Republicans more recently have moved right almost monolithically. On taxes, every congressional Republican voted against the Clinton 1993 budget plan and Obama’s health reform proposal that raised taxes, and virtually all Republicans backed the younger Bush’s tax cuts. Almost every House Republican from even the leafiest suburban districts voted with the National Rifle Association in 2011 to override state concealed-carry laws. And support for a pathway to citizenship for illegal immigrants grew so toxic inside the GOP that John McCain, during his 2008 presidential campaign, felt compelled to renounce his own 2006 legislation providing one. On all of these issues, Democrats remained split through the Bush years and Obama’s first term.
Now this unity gap is narrowing. On taxes, Republicans and conservatives are agonizing over whether to accept an increase not only in tax revenue but also in marginal tax rates–a party anathema since the 1990 deal. By contrast, Democrats are adamantly behind raising rates on the top earners. (If anything, Obama is courting resistance by setting the bar too high with this week’s offer to preserve current rates for those earning less than $400,000.) On immigration, Obama and congressional Democrats have signaled that they intend to move forward aggressively; the same trajectory seems to be developing, in a more qualified way, on guns. On both issues, most Republicans will still oppose the Democratic initiatives. But unaccustomed cracks have emerged in that wall of opposition.
Shifting electoral incentives on each side are driving this role reversal. Overall, Democrats still operate as more of a coalition party, harboring a broader range of views, than Republicans. That’s largely because self-identified conservatives outnumber liberals in the electorate, which means that Democrats in most races (including the presidency) need to attract more votes from moderates to win than Republicans do.

Brownstein adds that “Democrats are now operating with a far more ideologically cohesive coalition that overwhelmingly supports action on issues that previously paralyzed the party.” He predicts “more polarization” in the short run, but sees Democrats as gaining more leverage to force reasonable compromises.
If Brownstein is right, then President Obama’s negotiation strategy makes sense. Offering concessions that many of his supporters oppose shows that he is at least negotiating in good faith, while Boehner is stuck with an increasingly unreasonable party that shows no interest in anything resembling a fair compromise.Whatever Obama gives up in the short run can be restored later, since demographics and souring public attitudes towards Republican obstructionism should help Democrats regain control of the House over the next two elections.