Newtons 3rd law states all forces come in pairs which act equally and in opposite directions. The magnet exerts a forward force on the truck and the truck exerts an equal force backwards on the magnet. Because the magnet is physically attached to the truck, there is no way for this to produce a non-zero net force on the system we are trying to move; so the truck will not accelerate.
This is similar to sitting on an office chair with your feet up and trying to push yourself forward by pushing on the back of the chair with your hands. Doesn't matter how hard you push, the chair will not want to accelerate.
The % is a little misleading though. The total # of people who self- identify as Republican has also been shrinking (true with people who self-identify as democratic too). More and more people self-identify as independent. Most of the data I have looked at stop at 2023-2025 though, so who knows what it'd look like today after the fiasco this administration has been in 2026.