Two candidates

Hillary Clinton finally announced that she would run in the 2016 Presidential election, and it looks like she might not have to face a serious primary contest,  while the Republican primary is expected to be "bruising". Wired predicts that Clinton will make gender issues key to her campaign (as part of a general focus on economic fairness and equity), Brooklyn Quarterly collects academic research into how the media treat female candidates differently (based on the depressingly few races that have happened). Over at SNL, Kate McKinnon is in for a good run over the next few years. 

Here's Hillary Clinton's first campaign video, titled Getting Started ("Hillary's running for president because everyday Americans need a champion" - note that "middle-class" has been replaced by a different term)

On the Republican side, Marco Rubio, Senator from Florida, declared he would run (Jeb Bush, Scott Walker and many others are also expected to announce, Rand Paul and Ted Cruz already have), making his youth and the idea of "generational change" central to his speech. NY Times' The Upshot debates his chances "in a deeply factionalized party", while FiveThirtyEight gives him a better chance. 

Here's VOX with some charts about how polarized voters are - and other significant features of current American politics.