Mark Halperin’s three things to watch for in politics for Wednesday, April 29.

1. Watch what happens today to mark President Obama’s 100th day in office. The president will be out on the road this morning with a town meeting in Arnold, Missouri. Then tonight at 8 pm ET, he’ll hold the third primetime presser of his short presidency at the White House. At both these events, watch to see what kind of message he drives and what tough questions he gets, both from ordinary people and reporters.

2. Watch the Arlen Specter story. The president and vice president welcomed him to the party earlier this morning at the White House. Watch to see if Republicans use today to start trying to rebuild the party or if they seem too caught up in their anger at Specter and their desire to rally the base rather than trying to grow the party.

3. Watch the progress on swine flu. The CDC announced the first U.S. death from the virus this morning and the White House is clearly trying to stay visible in the discourse on the story, with Obama expressing his condolences and addressing the crisis as a whole. Watch to see where that story heads and how big a story it is throughout the president’s day.