First, the message to Lincoln and below it is General McClellan's assessment referenced in the letter -

HEADQUARTERS ARMY OF THE POTOMAC.

Camp near Harrison's Landing, July 7, 1862.

President LINCOLN:

SIR: I beg to inclose a copy of a letter of this date from me to Major-General Pope, which shows the existing condition of matters in respect to my position and prospects and the morale of the troops as well as a more formal statement could do.

The enemy are disturbing my communications by firing with field batteries upon transports, creating some annoyance.

I am, sir, very respectfully, your obedient servant,
GEO. B. McCLELLAN.

Major-General, Commanding.

HEADQUARTERS ARMY OF THE POTOMAC.

Camp near Harrison's Landing, July 7, 1862.

Major General JOHN POPE.

Commanding Army of Virginia:

GENERAL: I have to acknowledge the receipt of your letter of the 4th instant, and to thank you for offers of co-operation and assistance. I cordially approve your project of concentrating your troops. The departure from this wise principle has been the cause of all our trouble in front of Washington. I cannot too strongly represent to you the pressing necessity there is for the rapid concentration of your forces, for it is not yet determined which policy the enemy intends to pursue, whether to attack Washington or to bestow his entire attention upon the army.

I am in a very strong natural position, rendered stronger every day by the labor of the troops, and which in a few days will be impregnable. I hope in the course of to-morrow to seize a position on the right bank of the James, which will enable me to use either bank of that river at will. I am pushing up supplies as rapidly as possible, in order to be perfectly independent of the navigation of the river until strong re-enforcements can reach me. The army is in admirable spirits and discipline. It would fight better to-morrow than it ever did before. I shall carefully watch for any fault committed by the enemy and take advantage of it. As soon as Burnside arrives I will feel the force of the enemy and ascertain his exact position. If I learn that he has moved upon you I will move upon Richmond, do my best to take it, and endeavor to cut off his retreat.

If you are not molested, I would urge that you lose not a day in the concentration of your troops, and at least push your cavalry so far forward as to partially divert the attention of the enemy from this army.

The Army of the Potomac has lost heavily in killed and wounded during the series of desperate battles which it has given during the past two weeks, but I repeat it is no way disheartened. Its morale, discipline, and desire to fight are not only unimpaired but increased. Although to insure success it is absolutely necessary that we promptly receive heavy re-enforcements, the spirit of this army is such that I feel unable to restrain it from speedily resuming the offensive, unless reconnaissances should develop so overwhelming a force of the enemy in front as to render it out of the question. Even in that event we will endeavor to find some weak point in the enemy's lines which we will attack in order to break it.

I would be glad to be in daily communication with you, both by telegraph and by letter.

I may say in conclusion that so far as my position is concerned I feel abundantly able to repulse any attack. I fear only for the other side of the river and for my communications.

To preserve the morale of my men I must maintain my present position as long as it is possible. Therefore I shall not fall back unless absolutely forced to do so.

Again thanking you for your cordial offer of support, I am, very sincerely, yours,
GEO. B. McCLELLAN,

Major-General, Commanding.