Shocking news Tuesday night: As the political world focused on Illinois primaries, word that former Sen. Dan Coats (R) will announce his candidacy for Senate tomorrow in Indiana, challenging incumbent Evan Bayh.

From the site Howey Politics:

The source, former aide Curt Smith of the Indiana Family Institute, said that Coats knows he has about two weeks to gather the 4,500 signatures - 500 per Congressional district - in two weeks.

Coats was up for re-election in 1998 when he decided to retire, citing the pressures of constant fundraising. Bayh went on that year to defeat former Fort Wayne Mayor Paul Helmke to reclaim his father's Senate seat.

Politico has confirmed the report.

Coats was the ambassador to Germany under Pres. Bush. After returning from that assignment, he was last seen in the public spotlight as the "sherpa" for the Supreme Court nomination of Harriet Miers, and then Samuel Alito in 2005.

The Coats candidacy will certainly put major pressure on Bayh, but an important note for the incumbent: he has just under $13 million cash on hand, the third-most of all incumbents in the Senate through the 2009 filings.