The Democratic Party strategy of (what I would call) remaining weak so Republicans don't attack them is logically fallacious. Republicans' entire platform is based on lying to people to manipulate them. They don't need "ammo" to attack the Democrats. They will, and do, simply lie.
Therefore, the notion that Pelosi is rejecting Medicare for All in order to protect the ACA is, to me, not likely. She receives a lot of money from the private insurance industry, which is the main beneficiary of the ACA. Obama and the Democratic majority that passed ACA also mostly took money from the private insurance lobby. A public option was in the ACA during the planning phase and it was Democrats that removed it. There is a history of Democrats fighting single payer, which happened recently in California.
Single payer has some popularity from Americans on the right, and it polls at something like a 60% approval rating nationally, and going up. Additionally, on another healthcare-related proposal earlier this year, 12 Republicans supported Bernie's proposal of importing cheaper drugs from Canada. It was 13 Democrats including Cory Booker (who received over $200k from big pharma from 2014-2016), who voted the proposal down. So the pressure has to come from the people to pass something like Medicare for All. Weak strategies aren't actually pragmatic, they are merely weak strategies that enable the Republicans to radicalize, and may have helped Democrats lose over 1000 seats at the state and federal levels over the passed 8-9 years.
