Cauchon was a Chrétien loyalist and opposed Paul Martin's attempt to force Chrétien to retire.
When Chrétien announced his resignation, Cauchon was touted as a possible candidate to succeed him but did not end up running in the 2003 leadership election.
Cauchon refused to back Martin's leadership bid, and decided to support John Manley.
Martin was elected leader and did not include Cauchon in his cabinet.
Following this he announced he would not seek re-election in the 2004 federal election.

Cauchon was considered a potential candidate in both the 2006 and 2009 Liberal leadership elections, however in both cases he announced he would not run.
In 2006, he endorsed former Ontario Premier Bob Rae who placed third.

At the Liberal Party's 2012 biennial convention, Cauchon hosted a hospitality suite leading to speculation that he was interested in running for leader in the 2013 leadership election.
In December 2012, it was reported that Cauchon was planning a lately entry into the race after some Liberals feared the top tier of contenders were supporting right-wing policies.
On the last weekend before the registration cutoff on January 14, 2013, Cauchon was trying to gather the 300 signatures needed to enter the leadership race.
Fellow leadership contender David Bertschi sent out an email to Liberals asking for their help to get enough signatures so that Cauchon could enter the contest.
On April 14, 2013, he lost the leadership election to Montreal MP Justin Trudeau.
Cauchon was a Chrétien loyalist and opposed Paul Martin's attempt to force Chrétien to retire. When Chrétien announced his resignation, Cauchon was touted as a possible candidate to succeed him but did not end up running in the 2003 leadership election. Cauchon refused to back Martin's leadership bid, and decided to support John Manley. Martin was elected leader and did not include Cauchon in his cabinet. Following this he announced he would not seek re-election in the 2004 federal election.
Cauchon was considered a potential candidate in both the 2006 and 2009 Liberal leadership elections, however in both cases he announced he would not run. In 2006, he endorsed former Ontario Premier Bob Rae who placed third.
At the Liberal Party's 2012 biennial convention, Cauchon hosted a hospitality suite leading to speculation that he was interested in running for leader in the 2013 leadership election. In December 2012, it was reported that Cauchon was planning a lately entry into the race after some Liberals feared the top tier of contenders were supporting right-wing policies. On the last weekend before the registration cutoff on January 14, 2013, Cauchon was trying to gather the 300 signatures needed to enter the leadership race. Fellow leadership contender David Bertschi sent out an email to Liberals asking for their help to get enough signatures so that Cauchon could enter the contest. On April 14, 2013, he lost the leadership election to Montreal MP Justin Trudeau.
Martin Cauchon