That is a good question, especially from the point of view of having so many assumptions that are not based in our reality in the United States of America but in the quasi-reality of the national media.
There is no "The Democratic Party." Political parties in the United States are based in the individual states. For example the name of the Democratic party in the State of Minnesota is the Minnesota Democratic-Farmer-Labor Party (DFL.)
Your question appeared very strange from my view point. I live in Texas. Texas hasn't voted in a state-wide Democrat to office since 1994. Not a very successful Democratic Party.
Because journalists are fundamentally lazy people they speak in national terms ignoring the truth behind their words. And because we either don't teach or everybody is asleep in civics class these days few Americans are capable of independent thinking or analysis.
Your question brilliantly exposes this situation.
The best answer is that more people in populous states vote their convictions and those convictions best match the programs and policies of the Democratic Party in their state.
Grover Cleveland was the first successful presidential candidate of the modern Democratic Party- maybe you could say he created it.
Thomas Jefferson.
Who started the Democratic Party? Who started the Democratic Party?
The Democratic-Republican Party was the forerunner of the Democratic Party. It was started by Thomas Jefferson.
There is no supervisor for the Democratic party.
What did the Democratic Party and the Whig party have in common
The Democratic Party supports Obama for President. The Democratic Party will not be bullied by Republicans.
The Democratic Party is Washington State's Majority party.
the Democratic Party.
Harry S. Truman was a part of the Democratic party.
Democratic Party - Singapore - was created in 1955.
Democratic Union Party was created in 1947.