After what happened at The First Battle of Bull Run? No way! Let's train our soldiers some more.
I'm tired of watching the soldiers do drills. Let's launch a campaign to fight the Confederacy.
McClellan's plan was to ferry his troops into the Chesapeake Bay then it would simplify the march but it would not protect Washington.
Lincoln's plan was to march McClellan's troops through Manassas that way the troops would stay between the capitol and Richmond.
And took 90,000 men with him on the ferry.
McClellan left 40,000 troops in Washington.
Upon reaching the other side of the Bay, Magruder, the Confederate general, paraded his 15,000 men visibly around McClellan's troops. To McClellan it seemed like Magruder had way more troops than him so he waited a month to get more troops.
When the troops actually came, Magruder's troops retreated the short distance to Richmond.