At this point, it’s even more difficult than that. You can have an amazingly popular candidate that is a shoe-in for the POTUS vote… and they will be absolutely ineffective without the massive political machine that is the DNC/RNC backing them up. It’s not just the house and senate seats, it’s state government, municipal government, etc that also need representation by your new party. Tens of thousands of people need to be elected in positions in all levels before a new party gains enough political clout to even think about operating collectively at the national level.
Not to mention the fact that the judicial branch will still be packed with lifers with loyalties to the two incumbent parties.