This. Or, cough up the change + fare diff. DCA to IAD by ground is miserable and stressful to make a three hour connect where you have to clear security again in a different airport. Depending on the time of day, having TSA Pre at IAD can make little to no difference.

It's do-able (generous adjective..). But, I value my time and sanity and would opt for any alternative for avoiding the ground game.