Both candidates in the new 11th Congressional District have evolving views on gay marriage, including opinions that have changed since February.
The district was drawn by Illinois Democrats, and is generally a more liberal district than either candidate has campaigned in during past elections.
Republican Judy Biggert answered a Daily Herald questionnaire in February by saying whether to legalize gay marriage is up to the states, not the federal government to decide.
"Nothing related to marriage -- not even the prohibition on bigamy or polygamy -- is addressed in the Constitution," Biggert said. "Marriage should be kept out of the Constitution and the states should continue to exercise what is best left to the states."
In a recent television debate on WTTW, Biggert said she's starting to think of laws against gay marriage as discrimination.
However, there are legal issues to sort through before gay marriage would have her full support.
"I support civil unions," Biggert said. "I'm close to reaching for the gay marriages -- to say that that's fine. But as a lawyer, and having worked with estate planning, we really need to see how that would work."
In Congress, Biggert has been more supportive of gay rights than some of her Republican peers.
She voted to prohibit job discrimination based on sexual orientation.
She voted against Constitutional amendments to define marriage as a contract between one man and one woman and an amendment to outright ban same-sex marriage.
She also voted against a ban on gay adoption in Washington, D.C.
However, Biggert has opposed the repeal of the Defense of Marriage Act, which bans federal recognition of same-sex marriage.
The law has prevented same-sex couples who have married in one state from having that marriage recognized in other states.
Biggert is now comparing her view of gay marriage as an issue that triggers her own memories of being discriminated against for being a female law student.
"I don't want to see discrimination against anyone," Biggert said.
In recent weeks, Foster has said his support for gay marriage "is not ambiguous."
But like Biggert, that is also a recent change toward a more liberal point of view.
In his February Daily Herald candidate questionnaire, Foster maintained the same point of view he took during his re-election bid in the 14th Congressional District race a couple years ago.
"I believe marriage is between a man and a woman, but that gay couples should be able to receive all of the rights and benefits of marriage in the form of civil unions," Foster wrote.
In an endorsement interview last month, Foster explained he's had a change of thinking. He now fully supports gay marriage.
"I know everyone's attitudes are evolving on this," Foster said. "I was always a strong supporter of the civil unions that gave 100 percent of the legal requirements.
"So what was left is a discussion about a label rather than anything that would have operational, legal significance. During the time of the economic crisis I thought that prioritizing a very divisive discussion about a label wasn't the time for it.
"But life goes on, and society evolves. I had realized it was time to change my position on that."