Mr. Clay's letter opposing the annexation of Texas, unlike the letter of Mr. Van Buren, brought its author strength and prestige in the section upon which he chiefly relied for support in the election. He was nominated with unbounded manifestations of enthusiasm at Baltimore, on the first of May, with no platform except a brief extract from one of his own letters embraced in a single resolution, and containing no reference whatever to the Texas question. His prospects were considered most brilliant, and his supporters throughout the Union were absolutely confident of his election. But the nomination of Mr. Polk, four weeks later, surprised and disquieted Mr. Clay. More quickly than his ardent and blinded advocates, he perceived the danger to himself which the candidacy of Mr. Polk inevitably involved; and he at once became restless and dissatisfied with the drift and tendency of the campaign. The convention which nominated Mr. Polk took bold ground for the immediate re-annexation of Texas and re-occupation of Oregon. This peculiar form of expression was used to indicate that Texas had already belonged to us under the Louisiana purchase, and that Oregon had been wholly ours prior to the treaty of joint occupancy with Great Britain. It further declared, that our title to the whole of Oregon, up to 54 deg. 40' north latitude, was "clear and indisputable"; thus carrying our claim to the borders of the Russian possessions, and utterly denying and defying the pretension of Great Britain to the ownership of any territory bordering on the Pacific. FATAL CHANGE IN MR. CLAY'S POSITION.