Paul Ryan's presidential aspirations on hold

Rep. Paul Ryan, R-Wisconsin, the 2012 vice presidential nominee, said Monday that he won't run for president in 2016.

"I have decided that I am not going to run for president in 2016," he told NBC News in a phone interview. Ryan said made the decision weeks ago and is "at peace" with the move.

He then posted his decision on Twitter, citing the demands of his new job as chairman of the powerful House Ways and Means Committee.

House Ways and Means is the committee that writes all of the nation's taxes, and demands so much attention that its members are generally only allowed to serve on this committee.

• Paul Ryan airs frustrations with GOP in new book
• Congressman Paul Ryan's journey from the sandbox to the spotlight

Ryan, who was re-elected to his ninth term in Congress last November, was GOP nominee Mitt Romney's running mate in 2012. Although he kept presidential speculation alive, even writing a book with policy prescriptions for his party last year, he also seemed more ambivalent than some of his peers about the prospect of a presidential campaign in 2016.

He made no secret of the fact that he had his eye on the chairmanship of the House Ways and Means Committee, once term limits prevented him from serving another term in his previous job, chairman of the House Budget Committee.