So there you have it. In his testimony before the Joint Congressional Committee on the Conduct of the War, Irvin McDowell laid the failure at Bull Run squarely on the shoulders of Winfield Scott and Robert Patterson for their inability to hold the force of Joe Johnston in the Valley. And he made a convincing case, one that has held up to the present day. McDowell asserted that he was assurred by Scott that Johnston’s force would not join with Beauregard; McDowell planned accordingly; and his plans were only foiled by the arrival of Johnston’s men on the plains of Manassas, or rather the failure of Scott to live up to his part of the bargain.
On the surface, it seems to make sense. That is what happened. Beauregard would have been very hard pressed to defeat McDowell without the help of the Army of the Shenandoah. But look at what McDowell was saying – his plans were fine. He outlined the plan in his testimony, but he didn’t delve into one specific: how many of the enemy did he anticipate he would face? If we work backwards, and say he actually faced 35,000 (a round estimate), and Johnston added 8,000 to 12,000, then Beauregard without Johnston was 23,000 to 27,000. So if McDowell anticipated facing 27,000 or so, his argument holds water. But as noted in his plan, McDowell estimated the Confederate strength would equal (after reinforcements from all available quarters except those occupied by Patterson and by Butler at Fortress Monroe) about 35,000, or about the number with which he in fact did have to contend.
For me, the argument that Johnston’s arrival won the battle is sound, but the conclusion that it was all that upset McDowell’s plans does not pass the smell test. It’s spin, double-talk, newspeak, whatever you want to call it. And it’s firmly entrenched.