Sen. Mark KirkMark KirkObamaCare repeal bill would defund Planned Parenthood Leaked ObamaCare bill would defund Planned Parenthood GOP senator won't vote to defund Planned Parenthood MORE (R-Ill.) begins 2015 with a $2 million war chest, as he heads into what's likely to be a tough reelection fight.

The top-targeted GOP senator raised more than $600,000 from October through December 2014, according to Crain's Chicago Business.

That's a solid haul for a candidate not up for reelection during a fundraising quarter when others were scrambling for last-minute cash, though he (and his opponents) will have to raise much more than that each quarter to stay competitive.

Kirk's most likely opponent, Rep. Tammy Duckworth (D-Ill.), heads into 2015 with more than $1 million in the bank after raising $460,000 over the same time period.