McClellan, having 90,000 men, wanted Pope to reenforce him with his
45,000, and thus insure a renewal of his campaign against Richmond.
But this, of course, did not suit Pope who wished McClellan's army
to reenforce him and march to victory under his banner. But while
each of the rivals was insisting that his plan should be adopted
and Halleck, who held the chief of command, was wobbling between
them, trying to make up his mind to favor one or the other, Lee
took the whole matter out of his hands and decided it for him. He
did not want McClellan to be reenforced; first, because he was the
abler officer and, second, because he had or soon would have more
than sufficient men to capture Richmond and might wake to a realization
of this fact at any moment. From the Confederate standpoint it
was much safer to have Pope reenforced, for he did not have the
experience necessary to handle a large army. Therefore, the more
troops he had to mismanage the better. Moreover, Lee knew that
McClellan would cease to be dangerous as soon as he was obliged to
send any part of his forces away, for, as usual, he imagined that
his opponents already outnumbered him and that the withdrawal of
even a single regiment would place him practically at their mercy.

Carefully bearing all these facts in mind and thinking that it was
about time to force Halleck to transfer some of McClellan's troops
to Pope, Lee ordered Jackson to attack the man who thus far had
seen "only the backs of his foes." But at the Battle of Cedar
Mountain, which followed (August 9, 1862), his enemies would not turn
their backs and the fact evidently alarmed him, for he immediately
began shouting lustily for help. Perhaps he called a little louder
than was necessary in order to get as many of his rival's men as
possible under his own command, but the result was that McClellan's
army began rapidly melting away under orders to hurry to the rescue.