1. Approve the U.S membership in the League of Nations.
2.Ratify, or Approve the Treaty of Versallies.
The US Senate can refuse to confirm appointments to the Judicial Branch.
They felt that they didn't have a voice in the Senate.
Wilson refused because Huerta had murdered Mexico's former leader Fransisco Medeo in a coup. Wilson refused on the grounds of his "moral" diplomacy.
The Allies refuse to accept a negotiated peace settlement presented by the Central Powers because they could not trust in their willingness to fulfill the terms. Germany was in particular deemed untrustworthy.
According the United States Constitution, the US Senate can refuse the president's appointments. It can also reject treaties that have been agreed to by the president.
He refuse to extend civil rights to African Americans
The House of the Senate might refuse to assign a number to it.
The Legislative branch, specifically the Senate
It was the tribunes who could veto the actions of the senate (or any other magistrate except a dictator) if they were not in the best interests of the people.
They rejected any treaty that included the league of Nations.
If you referring to the Christian song with the chorus; "I don't want to live like I don't care. I don't want to say another empty prayer. Oh I refuse to, sit around and wait for someone else, to do what God has called me to do myself. I could choose not to move; but I refuse!" The song is I Refuse by Josh Wilson.
Although the US President Wilson had been pivotal to the peace treaty negotiations which included setting up the League of Nations that was to prevent further wars, the US Senate refused to ratify the Treaty of Versailles. There were strongly isolationist tendencies there which made the Senate shrink away from having to become involved with worldwide peacekeeping. Therefore the US never joined the League of Nations.