The nickname was originally used by Southern Democrats. After the Republicans won back the Presidency and Congress for the first time since the Grant administration, the Chicago Tribuneproclaimed: "Let us be thankful that under the rule of the Grand Old Party ... these United States will resume the onward and upward march which the election of Grover Cleveland in 1884 partially arrested."
The history is not perfectly clear, but the link below provides the official explanation by the Republican Party.
Although GOP does stand for Grand Old Party, it only refers to the Republican Party not the Democratic Party.
The Republican Party of the United States is known as the Grand Old Party.
GOP means the "Grand Old Party" or as almost everyone calls it the "Republican Party"
The Republican Party is also known as the Grand Old Party (GOP).
GOP which at first may have stood for "Gallant Old Party" but now stands for "Grand Old Party" has been used since the 1876 Convention in Cincinnati if not before.
The Grand Old Party or GOP
Grand Old Party Gallup Opinion PollGrand old Party
An old term used to refer to an evening party is "soiree".
The Grand old Party or GOP
Grand Old Party
grand old party