PHILADELPHIA -- The team Barack Obama put in charge of finding his runningmate has suffered a blow. 

Now, the the shakeup has sparked a new round of political jabs between Obama and his GOP rival John McCain.

Following days of criticism that he cashed in on the nation's mortgage crisis, Jim Johnson, a member of Obama's vice presidential search team, has resigned.

Johnson's resignation comes after days of Republican criticism.

At the center of the controversy are published reports that Johnson used his connections at mortgage company Countrywide to get  good deal on a home. Johnson denies doing anything illegal. Countrywide is being investigated for its alleged role in the subprime mortgage crisis, and has often been criticized by Obama himself.

Responding to the resignation, Obama said, "Jim did not want to distract in any way from the very important task of gathering information about my vice presidential nominee, so he has made a decision to step aside that I accept."

Quick to attack, the McCain camp said the resignation raises questions about Obama's judgment.

"The American people have reason to question the judgment of a candidate who has shown he will only make the right call when under pressure," McCain said.

Johnson's resignation comes as Obama continues touting his economic plan. In Chicago Wednesday, he accused McCain of doing little to help Americans in debt, and called for tougher restrictions on credit card companies.

"I've proposed a credit card bill of rights. The first thing we'll do under this bill of rights is ban unilateral changes to credit card agreements. You should pay the rate you signed up for," Obama said.

Trying to pick up votes in battleground states like Pennsylvania, McCain reminded a Philadelphia crowd of controversial comments his rival made in April about small-town voters.

"I don't agree with Sen. Obama that they cling to their religion and constitution because they are bitter," McCain said.

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