While most upcoming elections are designed to help set government’s course in 2011, Washington Examiner chief political correspondent Byron York addresses today a race that could have a more immediate impact: the race to replace Joe Biden in the U.S. Senate.

The winner will take office immediately after the Nov. 2 election to fill the last four years of Biden’s unexpired term. Republicans vying for the seat offer very different alternatives:

[Christine] O’Donnell is running for the Republican nomination against GOP moderate Rep. Mike Castle. If Castle wins the Sept. 14 party primary, she argues, he could go on to win the general election and start voting with Democrats right away.

“Republicans have to decide, who do they want serving in that lame duck session?” O’Donnell asks. “Do they want Mike Castle, who voted for cap and trade, voted for TARP, voted for cash for clunkers, or do they want a true constitutionalist?”

There’s no doubt Castle is among the most liberal Republicans on Capitol Hill. In 2008, he received a rating of 28 (out of 100) from the American Conservative Union, while receiving a rating of 65 from the liberal Americans for Democratic Action. Most recently, he co-authored the DISCLOSE Act, which nearly all Republicans opposed.

O’Donnell is running on a solidly conservative platform, much like she did in 2008, when she challenged Biden and won just 35 percent of the vote. Now, her biggest job is convincing people that this race — a primary open only to Republicans — is one she can win.