WASHINGTON — Sen. Bob Casey said Friday he that he would not run for president in 2020, ending speculation he fueled by spending the last few months refusing to rule it out.

The Pennsylvania Democrat’s nearly 700-word statement laid out a litany of issues that he said made him consider a bid, from the plight of the middle class to the power of corporations and national security concerns stoked by President Donald Trump’s posture toward Russia.

“With all of these challenges confronting us, and with our commonwealth playing a potentially decisive role in the 2020 vote, I believed it was important for me to at least consider the monumental undertaking of running for president,” Casey said. “After two months of considering it, I have concluded that the best way for me to fight for the America that so many of us believe in is to stay in the U.S. Senate.”

He called the upcoming election the most important of “the modern era,” but said he was confident Democrats would nominate a candidate who could win the Keystone State, expected to be critical in the fight for the White House.

Casey had stoked speculation shortly after his November reelection by issuing a series of nondenials when reporters asked if he would consider running for president, though he mostly just said he was leaving the door open or considering his options.

Few, if any, people in the political world thought the low-key Casey would actually run, especially with so many more high-profile Democratic colleagues in the race. The senator had taken no serious steps toward running and had not contacted top Pennsylvania donors. He told the Inquirer and Daily News this week he was still “on Step One” of his thought process.

Several Pennsylvania insiders, however, speculated that Casey might make a reasonable vice presidential pick, given his six statewide wins in a big swing state and his appeal to the kind of working-class white voters who swung sharply to Trump in 2016. Casey won his third Senate term in November with a convincing 13 percentage point victory over Trump-backed Republican Lou Barletta.

Casey’s opposition to abortion, however, would be a major stumbling block in a Democratic primary. There are also other Democratic senators from the Upper Midwest, including Ohio’s Sherrod Brown or Minnesota’s Amy Klobuchar, who might offer voters similar appeal. Each is openly mulling a presidential bid.

Others from the area are also still in the mix. Democrats across the country are waiting on a decision from former Vice President Joe Biden of Delaware, who tops early polling. Sen. Cory Booker of New Jersey is expected to announce his run in the coming weeks.