Sen. Bernie Sanders’ decision Wednesday to end his 2020 presidential campaign unleashes former President Barack Obama to finally get off the sidelines and campaign to defeat President Donald Trump.

Obama stayed out of the primary out of deference to the many Democrats running when the contest started more than a year ago. With Sanders out, Obama is free to jump in for his former vice president, Joe Biden. A source told the Chicago Sun-Times that Obama and Sanders have had several conversations in recent weeks.

Even when it became clear last month that Biden would be the presumptive nominee, Obama was not going to make a move until Sanders, the independent democratic socialist from Vermont, folded his second run for the White House.

In a livestream from his home in Burlington, Vermont, Sanders, said, “As I see the crisis gripping the nation, I cannot in good conscience continue to mount a campaign that cannot win and which would interfere in the important work required of all of us in this difficult hour.”

And with that, Biden vaulted into the November general election.

Biden now “can fully focus on his strategy for beating Donald Trump in November,” said Sheila Nix, the chair of the Biden Illinois campaign.

Here’s what changed the instant Sanders stood down:

• Obama has been talking to the Democratic presidential players before they got in, while they were running and after they quit. Obama and Sanders have been talking. Obama will make a move soon.

To watch: If Obama directly takes on Trump and when.

• And what about the enormously influential former first lady Michelle Obama? She never stumped for the 2018 mid-term candidates. She didn’t want to get in the political fray and risk her powerful brand with the election a week before the launch of her memoir, “Becoming,” which became a global blockbuster.

• The Biden campaign can now work in tandem with the Democratic National Committee, which gives the presumptive nominee more resources and staff.

• Biden can now work more closely with House Speaker Nancy Pelosi and Senate Democratic Leader Chuck Schumer.

• The Biden campaign can start raising money for the general election campaign.

• The Biden campaign is now free to aggressively start wooing Sanders supporters. Biden has a lot of work to do to break through to the Sanders youth vote.

The Trump-Biden battle will be fought on unfamiliar terrain because of the lockdown imposed by the COVID-19 pandemic sweeping the globe, destroying the U.S. economy in its wake.

Indeed, we did not know it at the time, but the March 17 Illinois primary marked the last chapter in what was then — seems like three centuries ago — seen as normal campaigning.

On March 7, Sanders held what ended up being the last large presidential campaign rally, when thousands of backers cheered him on at Grant Park. No one realized the coronavirus outburst was lurking among the throngs of people who stood elbow to elbow.

The March 10 Biden Illinois team party in a Near North bar — to celebrate those primary night victories — was the last Biden event in Chicago with people.

By March 13, the new reality sunk in when Biden hosted his first virtual event of this new COVID-19 era, a Friday night webcast event aimed at Illinois voters.

Sanders did not focus on Biden Wednesday as he acknowledged what has been obvious for weeks.

The Vermont senator talked about his significant legacy.

Sanders has been influential as a presidential candidate and as a founder of a successful progressive movement. He has mainstreamed the issues of health care for all, free public college tuition, income inequality, the $15-an-hour minimum wage and the Green New Deal.

Sanders said he will continue on primary ballots to accumulate delegates to exert “significant influence” on the Democratic party platform and rules at the August convention.

Biden said in a statement, “While the Sanders campaign has been suspended — its impact on this election and on elections to come is far from over.” Watch to see when the Sanders and Biden teams can agree on terms for a unity event.

Clem Balanoff, the chair of the Chicago chapter of Sanders’ legacy movement organization “Our Revolution,” said, “Bernie moved the country to the left. Our job is to keep it there.’