The Republican Party has never liked Social Security. They voted against it when it was created, and as recently as the Bush administration they tried to privatize it (putting seniors at the mercy of Wall Street speculators). They have finally realized, at least for the time being, that the American people like Social Security and don't want it eliminated or privatized, so they are now trying a different tactic -- cutting Social Security benefits.
You may wonder why the Republicans would want to cut the benefits for Social Security -- a program that has worked exactly as designed and keeps millions of seniors out of poverty in this country. They are doing it to protect their only true constituency (the rich and the corporations). Republican administrations have borrowed billions of dollars from the Social Security Trust Fund, and they did it because they didn't want to have to tax the rich and corporations a bit more to pay for their excessive spending (military-industrial complex, unnecessary wars, etc.).
Now they don't want to pay all of that money back. They don't want to pay it back because that would require the rich and corporations to pay their fair share in taxes -- an idea that is anathema to congressional Republicans. They have a different idea -- to cut Social Security benefits, thus punishing poor seniors instead of asking the rich and corporations to pay taxes.
Of course, they won't admit that. Instead, they tell lies to the American people -- like Social Security is going broke, that it takes too much from federal spending, that the budget cannot be balanced without cutting Social Security, and that cutting benefits is the only way to save the Social Security program (which is laughable since they have done everything they can to destroy the program). These are nothing but lies told to justify their own hard-hearted greed. They are not true now, and have never been true. Here is the truth (from Social Security Works):
I would add one more point. The average Social Security benefit is slightly less than $1100 a month -- a pitiful sum considering the prices in our society. That means millions of seniors struggle to live on $13,000 a year or less. They simply cannot afford any kind of Social Security cut -- not even a small hidden cut like going from the inflation rate (CPI) for raises to a chained-CPI (which doesn't truly keep up with real inflation).
The Republicans have made it very clear that they don't care about America's seniors, and they are willing to toss seniors under the bus to reward the rich and corporations (the only entities in this economy who don't need any government help). We must stop their mean-spirited and misguided attempt to cut benefits and damage Social Security.