Maryland Gov. Martin O'Malley's approval ratings are falling as Bob Ehrlich edges ahead of his opponent in the race to win the Governor's Mansion, according to a new poll.

O'Malley's approval rating fell four percentage points to 50 percent in the last month, according to a Rasmussen telephone survey of 500 likely Maryland voters.

Analysts are tying O'Malley's falling popularity to Democrats' frustration with President Obama's administration.

"We've seen some levels of disappointment in the Obama administration among Democrats," said Jerry Pasternak, who served 12 years as senior political and policy adviser to former Montgomery County Executive Doug Duncan. "What has played out at the national level may be filtering down to the governor's level."

Obama's approval rating among Marylanders slipped with O'Malley's this month to 57 percent from 59 percent in February 2010.

However, Marylanders' opinion of Obama's job in office is still more favorable than the national opinion, which is averaging 49 percent, according to Rasmussen.

"General frustration with incumbents is a big issue right now," said Scott Rasmussen, president of the polling company. Ehrlich served as Maryland's governor from 2002 to 2006, but O'Malley's term endured the tougher years of the national recession, he said.