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Kathleen Lange, File, Associated Press
FILE - In this May 9, 2007 file photo, then-Maryland Gov. Martin O'Malley endorses Democratic New York Sen. Hillary Rodham Clinton's campaign for the 2008 presidency at City Dock in Annapolis, Md. More than a decade ago, Bill Clinton spotted a political star on the horizon, someone he predicted would go from a big-city mayor to a national leader _ maybe even to the White House. In the years that followed, Clinton and his wife, New York Senator Hillary Rodham Clinton, showed up time and again as their young ally rose up the political ranks, hosting fundraisers, headlining rallies, and connecting him with their sprawling network of political donors.

WASHINGTON — He was once one of Hillary Rodham Clinton's most loyal supporters. Now he hopes to become her chief rival for the Democratic presidential nomination.

A former Maryland governor and Baltimore mayor, Martin O'Malley is expected to announce his presidential campaign on May 30. That will transform a close relationship with the Clintons that dates back years.

More than a decade ago, Bill Clinton told O'Malley he had the potential to become president some day.

In the years that followed, the Clintons showed up time and again as their young ally gained stature, hosting fundraisers, headlining rallies and connecting him to their sprawling network of political donors.

Today, O'Malley says that while he has "tremendous respect" for the Clintons, Democratic voters deserve more than a coronation.