There are 600,000 people in each congressional district. Maybe 300,000 eligible voters in an average district, and with an average of 50% turnout, there are 150,000 votes in an average congressional race.
In a tight congressional election a month ago, the Democratic candidate lost by less than 400 votes -- but 18,000 votes just ... disappeared.
They use paperless touchscreen voting machines in that part of Florida, and there is absolutely no way to find out why 18,000 people who voted in the election (around 1 out of every 10 voters) didn't cast a vote in the congressional election.
The House can choose not to seat a new member (in this case, the Republican candidate) because the election was so broken.
Speaker Pelosi and the newly-empowered Democrats should stand up for democracy and refuse to certify a broken election. They should require a revote to make sure every vote is counted.
MoveOn.org is sponsoring a petition that you can sign here to Speaker Pelosi, but I'd suggest you also call your Representative and ask him/her not to certify the broken election in Florida and stand up for democracy.