Sen. Chuck Schumer (D-N.Y.) is officially Senate majority leader after the inauguration of Vice President Kamala Harris and the swearing-in of new Sens. Alex Padilla (D-Calif.), Jon Ossoff (D-Ga.) and Raphael Warnock (D-Ga.).

Why it matters: With a 50-50 Senate, Schumer will control a narrow majority with Harris as the tie-breaking vote. Democratic control of the Senate is crucial to President Biden's agenda, from getting his coronavirus relief proposal passed to forgiving student debt.

The big picture: After more than 20 years in the Senate, Schumer will be taking the position from Sen. Mitch McConnell (R-Ky.), who became majority leader in 2015.

• McConnell and Schumer met on Tuesday to discuss a power-sharing agreement for the new Senate and to sort out when to hold President Trump's second impeachment trial.

Context: The last time the Senate was divided 50-50 was in 2001, under former President George W. Bush. The Senate agreed on a power-sharing plan that gave Republicans "a narrow advantage on setting the agenda on contentious issues," Roll Call writes.

• Yes, but: The parties have become more divided since then and negotiations on how the power-sharing will work are likely to drag along, meaning Biden will not have any confirmed Cabinet members on his first day in office.

Go deeper: Schumer's m(aj)ority checklist