With a handful of new members in the Senate and increasing control of the Republican Party in the House, conservatives in Congress are preparing to flex their collective muscle to ensure their priorities are met. This move, however, threatens to undermine GOP control and split the party. Alexander Bolton reports in The Hill:

House conservatives on the Budget Committee have threatened to derail the Republican budget plan at a markup scheduled for today if the chairman and GOP leadership do not link it to budget reforms.

Conservatives continued to negotiate with party leaders and Chairman Jim Nussle (R-Iowa) late yesterday.

[...]

A Republican Budget Committee member, speaking anonymously, said he and four other members may decline to support the budget if it does not bring about reform. The committee has 22 Republicans and 17 Democrats, according to its website, so just three recalcitrant conservatives could sink the budget if Democrats vote en bloc.

Hensarling, Ryan and Reps. Scott Garrett (R-N.J.), Pete Sessions (R-Texas) and Gresham Barrett (R-S.C.), have been identified as the Budget Committee members most willing to use their leverage to enact reform.

The budget is not the only area of policy in which the Republicans might face defections from within their ranks. Rep. Mike Pence (R-IN), the chairman of the Republican Study Group, has made statements which, if followed through, threaten the President's chances at privatizing Social Security. The Hill's Peter Savodnik has this story:

On Social Security, the congressman [Pence] underscored that Republicans would oppose new taxes and raising the cap on eligible income to pay for reform. And he maintained that borrowing $1 trillion to pay for the transition costs of Social Security reform now would save trillions later, an argument made by leading reform proponents such as Sen. John Sununu (R-N.H.) and Rep. Paul Ryan (R-Wis.).

On Social Security, Senate Democrats are entirely opposed to privatization at this point, assuring a move will not take place (60 votes are necessary for passage, so up to four Dems could defect and the bill would still not become law). If, however, the Senate Dems break, partial privatization could occur. For this to happen, though, taxes will have to be raised. If Pence and his allies nix the tax increase in the House, privatization will not happen.