Liberals/Progressives need to start defending the programs that are important. I think we begin this with our strongest and most easily defended program: Social Security. We should learn from the path those against taxes have followed and build a wall around this program.
The reason I picked Social Security alone, and didn't include or choose Medicare/Medicaid is because of the strength of the program. Social Security has been running surpluses for its entire life. It has a huge trust fund. It is important for maintaining and supporting of retired workers.
Both Medicare and Medicaid will have to be changed in some way as the healthcare costs continue to explode. Forcing there to be no cuts or major changes to those programs would not be possible in the long run. This isn't true with Social Security.
Social Security taxes were raised in the 80's to build up that trust fund and ensure that the program would be healthy. Those surpluses were used to hide growing deficits and support across the board tax cuts. Those tax cuts end up overwhelmingly helping those that make above $108,000/yr, because they are offset by the Social Security funds.
My idea is not too original, but it could be implemented if we are willing to stand by our statements. We ask every elected Democrat to sign a pledge to not cut Social Security benefits through changing the retirement age or lessening the payments through either changing the formula for yearly adjustments or means testing. Adding a statement that would offer a list of acceptable ways to fix the shortfall, such as changing the cap to cover 90% of taxable earnings, removing the cap completely or perhaps including capital gains as part of the taxable income.
Any violation of this pledge by a Democratic Party member would have us run commercials against the member, run a primary candidate against them and work to remove them from the position. If we were able to get money donated for just this cause, we could exert pressure on all Democratic Party members. I think protecting Social Security is something we can all agree on and get behind.
We have had lawmakers sign pledges before, but they were always confident there would be no punishment in breaking them. We would have to follow through with this, and make sure to punish any candidate breaking this pledge.