The most effective way is likely not broad-based cuts but targeted cuts to old-age spending via means-testing to induce liquidation of 401(k)s or other savings or tangible property to pay for their own care. I feel the longer (and slower) this trainwreck proceeds, the more likely this outcome is palatable. Roughly 52% of retirees have 250k or more in savings [1]. It is far preferable to drawdown those prior to either cutting benefits or raising taxes.
[1] https://www.aarp.org/money/retirement/peak-boomer-readiness/