All things considered, Douglas’s line of argument was as well sustained as any presented by the supporters of the war.  The absence of any citations to substantiate important points was of course due to the impromptu nature of the speech.  Two years later,[225] in a carefully prepared speech constructed on much the same principles, he made good these omissions, but without adding much, it must be confessed, to the strength of his argument.  The chain of evidence was in fact no stronger than its weakest link, which was the so-called treaty of Santa Anna with the President of the Republic of Texas.  Nowhere in the articles, public or secret, is there an express recognition of the independence of the Republic, nor of the boundary.  Santa Anna simply pledged himself to do his utmost to bring about a recognition of independence, and an acknowledgment of the claims of Texas to the Rio Grande as a boundary.[226] Did Douglas misinterpret these articles, or did he chance upon an unauthentic version of them?  In the subsequent speech to which reference has been made, he cited specific articles which supported his contention.  These citations do not tally with either the public or secret treaty.  It may be doubted whether the secret articles were generally known at this time; but the open treaty had been published in Niles’ Register correctly, and had been cited by President Polk.[227] The inference would seem to be that Douglas unwittingly used an unauthenticated version, and found in it a conclusive argument for the claim of Texas to the disputed territory.

Mr. John Quincy Adams had followed Douglas with the keenest interest, for with all the vigor which his declining strength permitted, he had denounced the war as an aggression upon a weaker neighbor.  He had repeatedly interrupted Douglas, so that the latter almost insensibly addressed his remarks to him.  They presented a striking contrast:  the feeble, old man and the ardent, young Westerner.  When Douglas alluded to the statement of Mr. Adams in 1819, that “our title to the Rio del Norte is as clear as to the island of New Orleans,” the old man replied testily, “I never said that our title was good to the Rio del Norte from its mouth to its source.”  But the gentleman surely did claim the Rio del Norte in general terms as the boundary under the Louisiana treaty, persisted Douglas.  “I have the official evidence over his own signature....  It is his celebrated dispatch to Don Onis, the Spanish minister.”  “I wrote that dispatch as Secretary of State,” responded Mr. Adams, somewhat disconcerted by evidence from his own pen, “and endeavored to make out the best case I could for my own country, as it was my duty; but I utterly deny that I claimed the Rio del Norte in its whole extent.  I only claimed it as the line a short distance up, and then took a line northward, some distance from the river.”  “I have heard of this line to which the gentleman refers,” replied Douglas.  “It followed a river near the gorge of the mountains, certainly more than a hundred miles above Matamoras.  Consequently, taking the gentleman on his own claim, the position occupied by General Taylor opposite Matamoras, and every inch of the ground upon which an American soldier has planted his foot, were clearly within our own territory as claimed by him in 1819."[228]