It exposed him to the taunts of rivals and ill-wishers; justified them in calling him presumptuous, and gave them a plausible excuse when they accused him of jealousy.

What made it worse was, that his own large building, the Laurentian Library, glaringly exhibits all the defects he discovered in Sangallo's cornice.
I find it difficult to resist the impression that Michelangelo was responsible, to a large extent, for the ill-will of those artists whom Vasari calls "la setta Sangallesca." His life became embittered by their animosity, and his industry as Papal architect continued to be hampered for many years by their intrigues.

But he alone was to blame at the beginning, not so much for expressing an honest opinion, as for doing so with insulting severity.
That Michelangelo may have been right in his condemnation of Sangallo's cornice is of course possible.

Paul himself was dissatisfied, and eventually threw that portion of the building open to competition.

Perino del Vaga, Sebastiano del Piombo, and the young Giorgio Vasari are said to have furnished designs.