"I'm not vulnerable," Roberts told Politico in September. "I'm in a very strong position. But I'm not taking anything lightly. Marines don't do that. They take the hill."
In the lead up to his announcement Tuesday evening, Wolf has repeatedly attacked Roberts on budget- and health care-related issues. He's criticized Roberts for voting to raise the debt ceiling and supporting the Wall Street bailout.
Wolf is related to the president through Wolf's great-grandfather, Thomas Creemore McCurry, who is also Obama's great-great-grandfather. Wolf's mother and Obama's mother were friends in Wichita, Kansas while she was growing up, according to National Review.
Wolf plans to announce his candidacy at a campaign event at Overland Park, Kansas at 7:30 CST.