WASHINGTON — Billionaire media mogul and former New York City mayor Michael Bloomberg says he’s decided against mounting a third-party bid for the White House. Bloomberg has spent months mulling an independent campaign. He made his decision official on Monday in a column posted on company’s BloombergView website. A Democrat-turned-Republican-turned independent, Bloomberg had set a mid-March deadline to make a decision about running so as to have enough time to make all 50 state ballots.