May 16, 2013 -- It appeared that President Obama had taken decisive action late Wednesday when he announced that Treasury Secretary Jack Lew had demanded the resignation of acting IRS Commissioner Steven Miller amid the growing scandal over targeting conservative groups. But it turns out that Miller was subject to a term limit that would have forced him out of the job in three weeks.

Miller, a 25-year career IRS employee, was appointed acting commissioner on November 9, 2012. According to the Federal Vacancies Reform Act of 1998, his 210-day term would have set his last day in that post as June 8.

This does not mean that Miller is not paying a price. His intention had been to go back to his job as Deputy Commissioner for Services and Enforcement, a position that put him in charge of the tax exempt unit at the center of a scandal over targeting conservative groups.

This statute makes it clear Miller could not remain acting IRS commissioner unless he was proactively reappointed as acting commissioner for another 210 days, or Obama nominated a permanent commissioner allowing Miller to remain in the job until that person was confirmed.

A Treasury Department official points out, however, that under the law Miller would have continued to run the IRS from his deputy commissioner post.

READ OUR FULL COVERAGE OF THE IRS SCANDAL

In his resignation letter, Miller alluded to the fact that his term as acting commissioner was soon to expire.

"It is with regret that I will be departing from the IRS as my acting assignment ends in early June," Miller wrote in his resignation letter on Wednesday. "This has been an incredibly difficult time for the IRS given the events of the past few days, and there is a strong and immediate need to restore public trust in the nation's tax agency. I believe the Service will benefit from having a new acting commissioner in place during this challenging period."

But Miller also suggested he would not be leaving the post right away.

"As I wrap up my time at the IRS," he wrote, "I will be focused on an orderly transition."