Former United States President Barack Obama described the toll that his presidency took on his marriage to Michelle Obama.

In his upcoming memoir, A Promised Land, the former commander in chief opened up about his eight years in office and challenges that his relationship faced as a result. Barack noted the former First Lady’s frustration with having to take a back seat despite her own achievements.

“Despite Michelle’s success and popularity, I continued to sense an undercurrent of tension in her, subtle but constant, like the faint thrum of a hidden machine,” Barack wrote. “It was as if, confined as we were within the walls of the White House, all her previous sources of frustration became more concentrated, more vivid, whether it was my round the clock absorption with work, or the way politics exposed our family to scrutiny and attacks, or the tendency of even friends and family members to treat her role as secondary in importance.”

He added that he would sometimes ponder about their days before he became president and that some nights, “lying next to Michelle in the dark, I’d think about those days when everything between us felt lighter, when her smile was more constant and our love less encumbered, and my heart would suddenly tighten at the thought that those days might not return.”

Michelle Obama previously revealed to Oprah that her husband’s political career created challenges in their marriage and led to the pair going to couple’s counseling.

A Promised Land will be released on November 17, and will touch on Barack’s 2008 election, racism, and Donald Trump.