Final answer:
John Tyler's failures included not addressing the issue of slavery in the territories acquired from Mexico, though he set the stage for Texas' annexation. Ulysses S. Grant, another president, faced unrelated challenges such as failed diplomacy with Santo Domingo and difficulties in promoting a humane Native American policy.
Step-by-step explanation:
John Tyler had several failures during his presidency. One failure was not addressing the issue of slavery in the territories acquired from Mexico, as the acquisition of lands from Mexico in 1848 led to intense debates over slavery, but Tyler was not in office at that time. However, it was under Tyler that the groundwork was laid for the eventual annexation of Texas, which was completed by his successor, James K. Polk. In contrast to Tyler's successor, Ulysses S. Grant had different challenges. Grant's administration was characterized by attempts to foster a policy for the humane treatment of Native Americans, which often ended in violence. Additionally, Grant was unable to secure the annexation of Santo Domingo due to his poor relationship with influential Senators. Furthermore, Grant struggled to resolve the economic challenges of his time, specifically related to Reconstruction in the South and the emergence of Liberal Republicanism, which underscored the complexities inherent in post-war governance.