NEW YORK (AP) — Former New York Mayor Michael Bloomberg is taking early steps toward an independent campaign for president, seeing a potential path to the White House amid the rise of Republican Donald Trump and Democrat Bernie Sanders.

The billionaire media executive, who served three terms as mayor, is said to be concerned by Trump's lasting hold on the Republican field and is worried about the impact of Sanders' campaign on Hillary Clinton's bid for the party's nomination.

Bloomberg has retained advisers and plans to conduct a poll after New Hampshire primary on Feb. 9 to assess the state of the race and judge whether there is an opening for an independent campaign, according to three people familiar with Bloomberg's thinking. They were not authorized to publicly discuss his efforts and spoke on condition of anonymity.

He has set a March deadline to decide on whether to enter the race, believing that doing so any later would not allow him access to the ballot in all 50 states, they said. The ex-mayor would strongly consider running if the general election looked like it could come down to Sanders and Trump or Texas Sen. Ted Cruz, but is not ruling out a campaign if Clinton is ahead on the Democratic side.

To prepare for a potential run, Bloomberg has instructed aides to research previous third-party runs and is said to be willing to spend up to $1 billion of his own fortune, estimated to be about $37 billion, to finance his campaign.

Bloomberg was a longtime Democrat who became a Republican to run for mayor in 2001 and later switched to be an independent.

His plans were first reported Saturday by The New York Times.

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Associated Press writer Lisa Lerer in Washington contributed to this report.

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