The Democratic Congressional Campaign Committee ( DCCC ) is employing an unusual tactic to blunt what it says is Republican meddling in its primaries: It has teamed up with the candidates it sees as the "strongest" in key battleground districts, launching joint ad buys to squeeze out its Democratic primary opponents. Why it matters: This practice has infuriated parts of the party, particularly the progressive wing. "If DCCC were a good judge of electability, then we wouldn't be in the mess we're in," said Ravi Mangla, a spokesperson for the progressive Working Families Party, in a statement to Axios.…