Congressional caucuses are groups of congress members who work together to complete similar legislative aims.
Some are bipartisan (the CLimate Solutions Caucuses)as well as including members of both houses (Congressional Black Congress)
Members of each party caucus elect a leader (majority/minority), planning the legislative agenda, coordinate the party for votes and debates, achieving party unity.
Speaker of the HoR is the most high profile role in Congress, elected by all members of the house, so belongs to majority party, maintains order when in session. Also chooses membership of committees.
If they belongs ot he opposite party to the president, they act as the main opposition.
Example: Nancy Pelosi first female speaker from 2007-2011, re-elected in 2019.
She lef House Democrats to impeach Trump in Dec 2019, also working with Republicans to pass bipartisan legislation (Trump’s revised trade deal with Canada and Mexico**