Norman Lear, One Day at a Time often tackled serious issues in life and relationships, particularly those related to second-wave feminism, and can be considered an example of the "dramedy" (hybrid comedy/drama) genre. In an ironic twist, during the 1979–1980 season, Mackenzie Phillips was dealing with drug addiction and entered rehab in 1980, thus reflecting the Alcoholics Anonymous central sobriety saying, "One Day at a Time." Stories depicting such events as weddings, births, and other important milestones frequently stretched over two-, three-, and four-part episodes. Theme song and opening credits The theme song for One Day at a Time, "This Is It", was composed by Brill Building songwriter Jeff Barry and his wife Nancy Barry, and performed by recording artist Polly Cutter. The opening credits were originally seen over a filmed sequence showing Ann, Julie, and Barbara excitedly moving into their new home. Later, the opening credits sequence mostly consisted of clips of each cast member taken from previous episodes. Casting Actors Bonnie Franklin, Pat Harrington Jr., and Valerie Bertinelli were the only cast members to remain with the series throughout its entire run. Lead actress Mackenzie Phillips was fired after the fifth season due to growing problems with substance abuse. She later returned in a frequent recurring role. Original cast member Richard Masur was written out early in the second season, but returned as a guest star in the sixth-season finale. Richard Masur played attorney David Kane, a love interest for the newly divorced Ann Romano, in the first season and left after the fourth episode of the second season. In a 2016 interview with The A.V. Club, he explained that David was constantly proposing marriage to Ann and she refused him every time. The actor became even further frustrated when Lear insisted that David and Ann's romance be unconsummated. His role was relegated to being a confidante to Julie and Barbara and an adversary to Schneider. After several disagreements with the direction Masur's character took, Lear agreed to write off David from the show but not entirely, per his appearance in the finale. After Masur's departure, the producers replaced the romantic interest with a comedic foil. That role was filled by actress and comedienne Mary Louise Wilson, playing as Ginny Wroblicki, a cocktail waitress who becomes Ann's neighbor, best friend and confidante. It was an unhappy casting change all around, as the show’s ratings began to decline soon