The Illinois lawmaker has broken with his party in the past on gun control issues, but this time he plays a key role in co-sponsoring a Senate effort to crackdown on gun trafficking. Of all the post-Sandy Hook gun legislation now awaiting votes in Washington, many see the proposed federal pinch on straw buyers as having the best chance of passage.
"I feel particularly burdened to make it happen," Kirk said.
Kirk is one of the co-sponsors of Senate Bill 54, which would make gun trafficking and straw purchases federal crimes with significant prison time.
"To set up straw purchase cases is virtually impossible," said Kirk.
Kirk, who met with Chicago's police superintendent Thursday morning to talk guns, broke with most fellow Republicans in supporting the plan to make trafficking and straw buys a federal rap. It has survived a committee vote, but tougher tests await.
"It will be picked apart by a gazillion people -- that my job is to make sure we have every concerted question answered," said Kirk.
If someone is legally able to buy a gun now, but gives it to someone who legally can't do the same, that's a felony. But local police argue that straw buys have largely been treated as a paperwork violations that often end in probation for the straw buyer.
Roseanna Ander of the University of Chicago Crime Lab sees a federal approach sending a message.
"To make them think twice, it's not worth going to prison for 15 years to supply a gun to somebody, and hopefully it'll staunch the flow of some of the guns winding up in the hands of criminals," said Ander.
"Too many guns on the street, too little punishment once we take those guns off the street," said Chicago Police Superintendent Garry McCarthy.
Opponents of the bill say its language is too broad, that it could have unintended consequences for gun dealers who have properly followed the law, and that there is sufficient state law now, but local prosecutors and judges have failed to do all they could.
Kirk remains optimistic.
"I want to do a one-two punch on the supply of weapons coming into Chicago and the organizations who are purchasing and bringing them in," Kirk said.
The NRA has floated some language that would raise the burden of proof for convicting a straw buyer. Proponents of the bill say that language would leave the measure toothless.
Kirk nonetheless believes it will survive intact, and he is also optimistic about universal background checks, though opponents have strongly argued that, at the end of the day, that will not happen.
Kirk also talked his public backing of same-sex marriage.
Since his 68-word blog post and radio interview earlier this week, Mark Kirk says his change on same-sex marriage has been greeted with an overwhelmingly positive reaction -- from the public and fellow politicians.
"I thought, like many Americans, we have friends and colleagues from work or church who are gay, and the thought of discriminating is an anathema," Kirk said.
The stroke, Mark Kirk says, has made him more compassionate -- perhaps less obligated to political ideology. And the movie Lincoln, he says, also played a role in changing his view on same-sex marriage.
"I would just say the Lincoln legacy would be freedom and respect and no discrimination," said Kirk.
Kirk said he has received "almost no negative reaction" from the public. Nor has there been, he says, any negative reaction from fellow Republicans, particularly on the state level, where a gay marriage bill awaits a vote.
Kirk says, however, "I have not been lobbying them on this issue," and he doesn't intend to.
The House sponsor of the marriage equality bill says he does not yet have the votes needed for passage. At this point, it's not clear what influence Kirk's change brings to that debate.
Though he says he is not lobbying, Kirk does impart this message:
"Go ahead and take my position," said Kirk. "You'll be surprised at how much support you'll get."
Kirk is one of two Republican senators supporting same-sex marriage. Thursday, another Senate Democrat, Bill Nelson of Florida, announced that he too is changing course.
Nelson is the ninth Democratic U.S. senator in the last week to change positions on same-sex marriage.