what is party realignment? and national party conventions?

Answer 1

Parties realign politically to meet the changing electorate. This year the Dems picked locally more conservative candidates in red states. So their members in Congress will be slightly more conservative than in the previous sessions.

Party conventions are held every 4 years to officially nominate candidates. Delegates are selected by primaries and caucuses. A majority is required to win. The convention also writes the party platform.