There's a lot of this going around on both sides. Some conservatives are threatening to primary Republicans who support the gun bill or immigration reform.
Now we have the spectacle of liberal interest groups threatening the same consequences for Democratic lawmakers who support the entitlement reforms in President Obama's budget.
A trio of liberal groups is warning Democratic lawmakers who back cuts to entitlements programs that they could face a challenge from the left in the next election -- but it's unclear how serious the threat is.
The Progressive Change Campaign Committee, Democracy for America, and MoveOn.org have released sharply worded statements putting Democrats on notice that support for President Barack Obama's budget - which proposes cuts to Medicare and Social Security - would be tantamount to betrayal.
PCCC, a prominent liberal group, also launched a website called NoBenefitCuts.com. It asks supporters to sign a petition pledging to "support primary challenges to congressional Democrats who support benefit cuts."