Thiru Vignarajah is joining the race for mayor, a month after taking initial steps to join a Democratic primary that includes Mayor Brandon Scott and former Mayor Sheila Dixon. The former deputy attorney general for Maryland and now four-time candidate for office in Baltimore said he was pushed to enter the race after two major events last week: the latest batch of campaign finance reports from his rivals, which he was less than impressed by, and the purchase of the Baltimore Sun by David Smith, the executive chairman of Sinclair Inc. The Hunt Valley-based company owns and operates more than 190 television stations, including flagship WBFF Fox45.