WASHINGTON — Michael Bloomberg, the billionaire former three-term mayor of New York City, has opted against mounting a third-party White House bid that could have further roiled this year’s already extraordinarily unpredictable presidential campaign.

Bloomberg, who has spent months mulling an independent campaign, made his decision official Monday through an editorial posted by the Bloomberg View.

‘‘There is a good chance that my candidacy could lead to the election of Donald Trump or Senator Ted Cruz,’’ Bloomberg wrote. ‘‘That is not a risk I can take in good conscience.’’

The former mayor — who had indicated he'd have spent $1 billion of his own money on the run — had set a mid-March deadline for his team of advisers to assess the feasibility of mounting a run, believing that waiting longer would imperil his ability to complete the petition process needed to get on the ballots in all 50 states.

Both parties will hold presidential primaries in Michigan and Mississippi on Tuesday. In addition, Republicans will vote in a primary in Idaho and caucuses in Hawaii.

Those close to Bloomberg’s thinking say the former mayor had believed the dominance of Donald Trump among Republicans and the rise of Bernie Sanders amid Democrats had opened a centrist lane for a nonideological, pragmatic campaign.

But Hillary Clinton’s string of recent victories has given her a firm grip on the lead for the Democratic nomination and is blocking Bloomberg’s possible path, aides to the mayor said.

The decision concludes Bloomberg’s third and likely final flirtation with a White House run, a possibility that had grown popular among New York’s business class and, the mayor’s aides had believed, could have resonated with moderates and independents across the nation dissatisfied with the polarization in Washington and the rise of the political parties’ fringes.

Aides to Bloomberg, the 74-year-old Democrat-turned-Republican-turned-Democrat-turned independent, have said their own polling suggested that Bloomberg had a viable path to the needed 270 electoral votes if Trump, whom had disgusted the ex-mayor with his inflammatory rhetoric, and Sanders were the nominees.

But an Associated Press-GfK poll conducted last month suggested that six in 10 Republicans and Democrats alike said they would not consider backing Bloomberg.

The day before Mississippi’s primaries, Cruz stood on a table and spoke to more than 200 people at a restaurant in Florence, Miss., a blue-collar suburb of Jackson. A 110-foot cross dominates the parking lot of the restaurant.

Cruz won rowdy applause by saying he will protect gun owners’ rights, eliminate the US Department of Education, and nominate strict constitutionalists to the Supreme Court.

Ohio Governor John Kasich said at a Michigan rally Monday that he shouldn’t have answered a question in last week’s debate about whether he would support Trump if he wins the GOP presidential nomination.

Pushed by a self-identified Democratic voter to retract his potential support for Trump, Kasich said he ‘‘shouldn’t have even answered the question’’ because he plans on ‘‘being the GOP nominee, not Donald Trump.’’

Kasich said Trump sometimes ‘‘makes it difficult’’ to support him. Kasich declined to engage on the questioner’s comments that Trump and his supporters are racists and bigots.

On the Democratic side, Sanders said Monday that rival Clinton has been mischaracterizing his position on the federal government’s 2008 bailout of the auto industry on the eve of Michigan’s presidential primary.

The Vermont senator said in Kalamazoo, Mich., that he voted in 2008 for the rescue of the auto industry in the Senate when it was a stand-alone issue and not included in a bailout for Wall Street. The Senate measure ultimately failed and President George W. Bush approved more than $13 billion in federal aid to the automakers.

Clinton accused Sanders of opposing the auto bailout during Sunday night’s presidential debate in Flint, Mich. The state is home to the US auto industry.

Clinton campaigned Monday in Grand Rapids, Mich., where she said that the FBI’s legal battle with Apple over an encrypted iPhone amounts to a difficult public policy dilemma.

Clinton told a small group at a technology company that there’s ‘‘got to be some way to protect the privacy of data information,’’ but also a way to ‘‘follow-up on criminal activity and prevent crimes of terrorism.’’

Federal authorities want Apple’s help in bypassing iPhone security features so they can attempt to unlock the encrypted phone. Apple and other tech companies have objected, arguing that the government essentially wants Apple to create a ‘‘back door’’ that could make all iPhones vulnerable to hacking.

Clinton said the ‘‘real mistrust between the tech companies and the government right now is a serious problem that has to somehow be worked through.’’

Clinton also questioned if there was a way to get this information ‘‘without opening the door and causing more and worse consequences.’’