It's not an either/or. The policy and politics are entirely harnessed together. And preserving Medicare will yield political benefits which will allow Democrats to defeat other Trump/GOP initiatives that will do the country grievous harm.
Trump's election has sprung into overdrive a debate we've been having in the world of politics for more than a year: Is Trumpism largely about economic distress tied to globalization and neo-liberal economics or is it mainly driven by a white racial backlash against minorities Trump supporters believe are cutting to the front of the line in the race for economic preferment and cultural centrality? I largely put myself in the second camp. But as I think most people realize, these are not mutually exclusive explanations. And whichever side of the equation you come down on, what the Democrats need are issues that cut across the regional/racial/class divide we saw in the 2016 election.
Medicare does that.
There are numerous fronts where Democrats will need to resist Trump and the Republican Congress. But to be really effective anywhere they will need to chalk up wins somewhere because all political power is unitary. A president can't suffer a deflating defeat in one area without it eroding his power in others. Victories operate in the same way. Power gained or lost in one sphere translates into every other.
Stopping Republicans on Medicare Phaseout will reduce their ability to push their damaging agenda on other fronts.
The final point should be the most obvious. Donald Trump won the presidency promising to defend the economic interests of ordinary people from the 'crooked' elite on Wall Street and in Washington. Whether or not he believes or believed that he has rapidly allied himself with the Paul Ryan privatizers who want to eviscerate the federal programs which are the bedrock of the American middle class. Social Security and Medicare are at the top of that list. If you look at the faces in the crowds at Trump's most poisonous speeches I guarantee that you that very few of those people thought they were voting to lose their Medicare.
Getting rid of or gutting Medicare is incredibly unpopular. It can only be accomplished by a mixture of bamboozlement, scare tactics and unified party government which will allow the GOP to push the change through regardless of public opinion. Saving Medicare or giving everything in the effort to do so is a tailor-made way for Democrats to cut across the Trump-Clinton divide and undermine the idea that Trump or the GOP have the interests of the middle class or really anyone but libertarians and the extremely wealthy at heart.
I'll summarize my point. Medicare is hugely important for everyone, for the reasons I noted above. But it should become a central focus even if those who don't see it as the most important issue because it is an issue where Democrats can score a win and in doing so they will empower the opposition to defeat the Trump GOP on other critical fronts. Critically, it is a cross-cutting issue. They will either drive a wedge between Trump and the GOP or undermine for many voters who supported Trump the belief that he cares about the needs of people like them.