Good for Senator Mark Kirk for becoming the second Republican in the United States Senate to endorse marriage equality:

When I climbed the Capitol steps in January, I promised myself that I would return to the Senate with an open mind and greater respect for others.

Same-sex couples should have the right to civil marriage. Our time on this earth is limited, I know that better than most.  Life comes down to who you love and who loves you back — government has no place in the middle.

This is significant, for several reasons. It comes as Illinois is close to passing its own law legalizing gay marriage, so it’s good to have such a high profile Republican in the state endorsing the idea.

What’s more, Kirk is not evolving in the matter Rob Portman did. For him, it’s not about realizing that prohibiting gay marriage is wrong because a family member turns out to be gay.

Perhaps most important, Kirk’s quote — “government has no place in the middle” — is effectively a declaration that government should not have the authority to prevent gay marriage. That would make Kirk the only Republican in the Senate who appears to believe state governments shouldn’t have the power to ban it. Kirk is not claiming that he personally supports gay marriage but that it should be left to states. Rather, he is claiming government shouldn’t exclude gays from the institution of marriage.

“He seems to go further than Portman and say that he doesn’t believe government has any business regulating civil marriage to exclude gay people,” prominent gay rights advocate Richard Socarides tells me. “That would put him squarely in the category of people who believe that all 50 states ought to treat gay people the same.”

That, of course, is the issue that’s currently before the Supreme Court. Justices who heard the Prop 8 and Defense of Marriage Act cases may well clarify their thinking on the question of whether banning gay marriage violate the equal protection clause of the Constitution, which would give advocates a powerful tool to overturn state laws banning gay marriage around the country.

Though Kirk didn’t frame his statement in these terms, it’s good to have a Republican in the Senate who is willing to go this far. Little by little.