U.S. Sen. Claire McCaskill dismissed on Monday rumors that she may be interested in a 2016 run for governor – 12 years after she lost her first bid for that job.

When asked if she was considering another run for governor, McCaskill replied, “I actually am not. I am very busy in my job” as U.S. senator.

“I am very happy in the job I have, and I am very lucky to have it,’’ she said in an interview with St. Louis Public Radio.

McCaskill, a Democrat, was alluding to her overwhelming re-election in 2012, largely because of the missteps of her Republican rival, then-U.S. Rep. Todd Akin, R-Wildwood.

But while circumspect about her political future, McCaskill minced no words about her concern about the influence of wealthy financier Rex Sinquefield, the state’s largest political donor.

Since Friday, Sinquefield has donated $3.7 million to two conservative independent groups – Grow Missouri and the state chapter of Club for Growth – that seek lower income taxes and fewer regulations. The groups are expected to be major players in this fall's elections.

“What Rex Sinquefield wants to do is, he wants to buy the legislature and put in his vision, which is no income taxes and really high sales taxes,’’ McCaskill said in an interview Monday. “The people that are going to be hurt the most by that are the members of these unions.’’

McCaskill was speaking after she’d addressed a closed meeting of Missouri labor leaders, who are convening at the downtown Crowne Plaza hotel. She said she brought up Sinquefield in her closed-door remarks.

“I think there is a direct frontal attack on the middle class in Missouri right now,” she said. “I think Rex Sinquefield and his billions of dollars are obviously being teed up to elect people who are more focused on lowering taxes for business and wealthy folks than they are the income disparity that is growing in Missouri.”

The growing divide between the rich and everyone else is “affecting our overall revenue growth, it’s affecting our ability to compete,” she said. “And one of the reasons that this disparity is getting wider and wider is because people who have collectively bargained for good wages and benefits have really been taken on by some people like Rex Sinquefield.”

"I don't think the majority in Missouri wants a billionaire buying the legislature,'' McCaskill added.

Says many GOP candidates are "very extreme"

On the political front, she said she would continue to campaign for fellow Democrats in the Senate who are up for re-election this fall. Many of them had come to her aid in 2012, when she was considered one of the most vulnerable Senate Democrats on the ballot.

McCaskill called for Democrats to continue to highlight the social conservatism of many Republicans. She noted, for example, the Missouri General Assembly’s action last week to reinstate a law that imposes a 72-hour waiting period in the state before the woman can obtain an abortion.

There are no exceptions in the measure for rape or incest. Legislators overrode Gov. Jay Nixon’s earlier veto of a bill, which now becomes law.

McCaskill pointed out that state Rep. Rick Stream, R-Kirkwood, voted for that restriction – and for another bill that expands gun rights in the state.

“I’ve looked at Rick Stream’s record in the Missouri legislature,’’ she said. “His record looks like Todd Akin’s record.”

“His position on women’s issues is very extreme,’’ McCaskill continued, taking note of the pivotal role that women voters may place in St. Louis County and elsewhere in November. “I think he’s a perfectly nice man, but his policies are way out of whack with most voters in St. Louis County.”

McCaskill added that she supports the Democratic nominee for county executive, Steve Stenger.

As for herself, McCaskill said she'll support the Democratic nominee for governor in 2016, and she acknowledged that Missouri Attorney General Chris Koster -- a former Republican -- "has done a good job of clearing the field."

She didn't mention that Koster has gotten donations in the past from Sinquefield.