WASHINGTON (Reuters) -Former U.S. President Donald Trump on Thursday joined an effort by a co-defendant in his Georgia election interference case to disqualify prosecutor Fani Willis and dismiss the criminal charges, according to a court filing. Trump co-defendant Michael Roman has alleged in previous court filings that Willis had an inappropriate relationship with Nathan Wade, the lawyer she hired to help run the criminal case. Trump’s defense team endorsed those claims and leveled new accusations that Willis, the district attorney of Fulton County, “inappropriately injected race into the cas…