Key TakeawaysJetBlue shares tumbled Monday after the company announced plans to raise over $3 billion in debt and received credit downgrades from major credit rating agencies.S&P Global and Moody's downgraded the company, while Fitch Ratings affirmed its rating.Moody’s said it will likely take the airline "a number of years" to sufficiently improve its operating profit and cash flow enough to merit an upgrade. JetBlue (JBLU) shares tumbled more than 21% in intraday trading Monday after the company announce ...