WASHINGTON -- Rep. Chris Murphy (D-Conn.) will announce on Thursday that he plans to run for the Senate seat being vacated by retiring Sen. Joseph Lieberman (I-Conn), several Democratic sources tell the Huffington Post. The announcement will make the Murphy the second lawmaker to enter the Democratic primary. Earlier in the week, Susan Bysiewicz, a thrice-elected former secretary of state, said that she intended to run for Lieberman's seat as well.