¿Qué significa it superseded the efforts already underway ?

See a translation

Green’s efforts to impeach Donald Trump failed simply because he didn’t have the votes, though some high-profile Democrats—including Jim Clyburn (D–S.C.) and Keith Ellison (D-Minn.)—did cast ballots in its favor. In all, 58 House Democrats voted for impeachment, though Minority Leader Nancy Pelosi (D-Calif.) opposed the measure. “Now is not the time to consider articles of impeachment,” said Pelosi in a joint statement issued with Steny Hoyer (D-Md.)

Another reason that Green’s effort stalled is that it superseded the efforts already underway as a part of the special counsel investigation being headed up by Robert Mueller. Despite indictments of four members of Trump’s cohort—including former national security advisor Michael Kelly—there’s speculation that what’s currently known of the investigation is only the tip of the iceberg. The most recent development is that Trump’s banking information has been subpoenaed from Deutsche Bank.