Independent Vermont Sen. Bernie Sanders officially launched a long-shot White House run Thursday, giving presumed Democratic front-runner Hillary Clinton another potential primary challenger, and the 2016 campaign field at least five major candidates from both political parties.

By roughly a month from now, that field may have doubled.

So who’s next?

Next week:

— Retired pediatric neurosurgeon Ben Carson (R)  is expected to announce a 2016 run on Monday after years of speculation about his presidential ambitions. Carson, who has never held public office, has positioned himself as a Washington outsider. He will be the first African-American candidate to launch a 2016 presidential campaign.

— Former Hewlett-Packard CEO Carly Fiorina (R) is also expected to launch a White House run Monday, following recent jam-packed swings through Iowa and New Hampshire. The first woman on the GOP side to announce a presidential run, Fiorina has strongly positioned herself as the (potential) candidate who could most effectively challenge Clinton on women’s issues.

— Former Arkansas governor Mike Huckabee (R) is hosting an event Tuesday in his birthplace of Hope, Arkansas – the same as former President Bill Clinton – that is expected to serve as the formal launch to his 2016 campaign.

Sometime in the next few weeks

— Former Maryland governor Martin O’Malley has been expected to make a presidential announcement sometime next month.

— New Jersey Governor Chris Christie, whose likelihood of running has shifted from near-certain to unlikely and back again, most recently said he would announce his decision sometime in late May or early June.

— Former Texas governor Rick Perry is also expected to announce if he will run sometime in May or June.

June and beyond

— Former Pennsylvania senator Rick Santorum launched a testing-the-waters account earlier this month, indicating he is leaning toward running. His team has said he will decide by late spring.

— Wisconsin Gov. Scott Walker has been aggressively fundraising and traveling in anticipation of a 2016 presidential run and his White House bid is essentially a sure-thing at this point. He will likely launch his campaign after the Wisconsin state legislature's work period ends in June.

— Louisiana Gov. Bobby Jindal, who has been a steady presence in early voting states, has said he will make up his mind about running sometime after the Louisiana legislative period ends in June.

— Former Florida governor Jeb Bush’s White House run is all-but-certain at this point, given his colossal fundraising operation and his aggressive travel schedule. Still, his announcement may not come until sometime this summer.

Still unclear:

— Former Rhode Island governor Lincoln Chafee launched a presidential exploratory committee earlier this month. His team indicated earlier this month that he will formally become a candidate at some point, but it is unclear when he might hold an official launch.

— Vice President Joe Biden fueled speculation about his 2016 presidential ambitions earlier this year by traveling to three early-voting states. The actual likelihood of a Biden presidential campaign remains unclear, but he will announce his decision sometime this summer.