WASHINGTON — Michael Bloomberg, the billionaire former mayor of New York City, is opening the door to a 2020 Democratic presidential campaign, warning that the current field of candidates is ill-equipped to defeat President Donald Trump.

Bloomberg, who initially ruled out a 2020 run, has not made a final decision on whether to jump into the race. If he were to launch a campaign, it could dramatically reshape the Democratic contest less than three months before primary voting begins.

The 77-year-old has spent the past few weeks talking with prominent Democrats about the state of the 2020 field, expressing concerns about the steadiness of former Vice President Joe Biden’s campaign and the rise of liberal Sen. Massachusetts Elizabeth Warren, according to people with knowledge of those discussions. In recent days, he took steps to keep his options open, including moving to get on the primary ballot in Alabama ahead of the state’s Friday filing deadline.

In a statement on Thursday, Bloomberg adviser Howard Wolfson said the former mayor believes Trump “represents an unprecedented threat to our nation” and must be defeated.

“But Mike is increasingly concerned that the current field of candidates is not well positioned to do that,” Wolfson said.

Bloomberg’s moves come as the Democratic race enters a crucial phase. Biden’s front-runner status has been vigorously challenged by Warren and Vermont Sen. Bernie Sanders, who are flush with cash from small-dollar donors. But both are viewed by some Democrats as too liberal to win in a general election faceoff with Trump.