When Justice Scalia died in February 2016, why didn't Obama nominate a progressive replacement while he still could instead of risking that the succeeding president nominates a conservative one, which ended being the case when Trump nominated Neil Gorsuch? Obama had almost a year to nominate him but didn't, allowing to lose a progressive seat on the SCOTUS.
He did nominate Merrick Garland but the Republican majority senate decided to do nothing about that nomination with the reason given that it was to close to the election. This behavior of the senate was highly controversial at the time. They said it was up to the voters to decide the next president who would fill that spot and after Trump won he picked Neil Gorsuch who filled the empty slot.
On March 16, 2016, President Barack Obama nominated Merrick Garland for Associate Justice of the Supreme Court of the United States to succeed Antonin Scalia, who had died one month earlier. At the time of his nomination, Garland was the Chief Judge of the United States Court of Appeals for the District of Columbia Circuit.
This vacancy arose during Obama's final year as president. Hours after Scalia's death was announced, Senate Majority Leader Mitch McConnell said he would consider any appointment by the sitting president to be null and void. He said the next Supreme Court justice should be chosen by the next president—to be elected later that year. Senate Democrats criticized the move as being unprecedented, and responded saying that there was sufficient time to vote on a nominee before the election.
Scalia's death brought about an unusual, but not unprecedented, situation in which a Democratic president had the opportunity to nominate a Supreme Court justice while the Republicans controlled the United States Senate. Before 2016, such a situation had last arisen in 1895, when a Republican-led Senate confirmed Democrat Grover Cleveland's nomination of Rufus Wheeler Peckham to the Court in a voice vote; conversely, in 1988 a Democratic-led Senate had confirmed Republican Ronald Reagan's nomination of Anthony Kennedy and in 1991, a Senate held 57–43 by Democrats nevertheless confirmed Justice Clarence Thomas.: 75–83 Political commentators at the time widely recognized Scalia as one of the most conservative members of the Court, and noted that—while many considered Merrick Garland a centrist, and he had been called "essentially the model, neutral judge"—a replacement less conservative than Scalia could have shifted the Court's ideological balance for many years into the future. The confirmation of Garland would have given Democratic appointees a majority on the Supreme Court for the first time since the 1970 confirmation of Harry Blackmun.
The 11 members of the Senate Judiciary Committee's Republican majority refused to conduct the hearings necessary to advance the vote to the Senate at large, and Garland's nomination expired on January 3, 2017, with the end of the 114th Congress, 293 days after it had been submitted to the Senate. This marked the first time since the Civil War that a nominee whose nomination had not been withdrawn had failed to receive consideration for an open seat on the Court. Obama's successor, Donald Trump (a Republican), nominated Judge Neil Gorsuch to fill the vacancy on January 31, 2017, soon after taking office.