In his congressional term, Knollenberg was known as a staunch supporter of the North American Free Trade Agreement, President George W. Bush's stance on protecting manufactured goods and for voting against expanding SCHIP in the later years of his career.

[6] In 2006, however, Knollenberg faced a tough campaign against Democrat Nancy Skinner, a liberal talk show host in the Detroit area, ultimately winning by six points.

[5] Two years later, in a more difficult election cycle for Republican candidates, Knollenberg lost re-election to former state senator Gary Peters.

He supported the North American Free Trade Agreement and led the campaign against President George W. Bush's steel tariffs.

[3] Democratic candidate Nancy Skinner, a popular former radio-talk show host in the Detroit area, was her party's nominee for the 9th district.

[13][5] Prior to 2006, Knollenberg's election was widely considered to be relatively easy given the traditionally Republican leanings of Troy, the largest city in his district.

[6] The narrowness of his 2006 reelection bid, combined with his district's changing demographics led the Democratic Congressional Campaign Committee to target him for defeat.

[19] Knollenberg had two sons, Stephen and Martin with his wife, Sandra "Sandie" Moco,[20] whom he married in September 1962 at St Frances Cabrini Church in Allen Park, Michigan.

[1] Knollenberg died on February 6, 2018, due to complications from Alzheimer's disease at a care facility in Troy, Michigan at the age of 84.