Former New York City Mayor Michael Bloomberg is reportedly reconsidering whether to run for president as former Vice President Joe Biden struggles to pull away from Sen. Elizabeth Warren in the polls.

Bloomberg announced in March that he was not running. But according to CNBC, Bloomberg has told associates in recent weeks that Biden's struggle to maintain his lead against a surging Warren has brought second thoughts.

According to a national polling average by Real Clear Politics, Biden leads Warren 29.6% to 23.4% as of Sunday. As recently as Oct 7, Warren had been trending up and narrowly led Biden in the same national polling average.

However, Warren is currently leading Biden in polling averages in the first two primary contests: Iowa (Warren 22.7% to Biden 19.3%) and New Hampshire (27.3% to 24.3%). According to NPR, Bill Clinton is the only candidate in the last 43 years to lose Iowa and New Hampshire and still win the presidency. 

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Biden is also under constant attack from President Donald Trump. That includes questioning the international business dealings of Biden's son, Hunter. Trump's July 25 phone call to Ukraine's president about looking into the Bidens ultimately led to the House of Representatives launching an impeachment inquiry into Trump.

CNBC reports Bloomberg could decide to jump in if Biden decides to drop out before the primaries or struggles in the early contests. Bloomberg is worth $51 billion, according to Forbes, so he could self-finance a campaign.

Like Biden, Bloomberg would be seen as a moderate Democrat with immediate name recognition. Warren is seen as more progressive and farther to the left.

But one of Bloomberg's allies reportedly said it would only happen if Biden were to drop out.

Bloomberg has been a Republican and an independent, but has previously stated he would run as a Democrat if he jumped in the race.