I am not familiar with Cass, but if the comparison is with Bryan and McGovern, I am fine with it.
http://www.huffingtonpost.com/rich-rubino/party-loyalty-pays-off-fo_b_2406514.html
Party Loyalty Pays Off for John Kerry
Nominated by Barack Obama to serve as U.S. Secretary of State, John Kerry is one of a cavalcade of losing Democratic presidential nominees whose political careers have seen a second life. In 2004, had less than 60,000 votes in Ohio changed hands, Kerry would have been the first person to defeat a wartime President in U.S. history. Instead, Kerry returned to the work in the U.S. Senate, winning reelection in 2008 and securing the gavel of the Senate Foreign Relations Committee.
Kerry is not the first losing Democratic presidential nominee to be nominated as Secretary of State. William Jennings Bryan, who was the Democratic Party's standard-bearer in three elections, became Secretary of State under Woodrow Wilson. There is an eerie similitude between Bryan and Kerry. In 2007, Kerry, seen by many as the epitome of the old guard Democratic establishment, bucked the Democratic establishment candidate, U.S. Senator Hillary Clinton, in favor of the insurgent, U.S. Senator Barack Obama. Similarly, Bryan endorsed Wilson's bid for the Democratic Party nomination in 1912 over the putative frontrunner, House Speaker Champ Clark of Missouri. Bryan's endorsement helped Wilson secure enough delegates to be nominated on the 46th ballot at the Democratic Convention.
Obama, like Wilson, had a meteoric rise to winning his party's nomination. Wilson had just been elected to his first political office (Governor of New Jersey), only two years earlier. Obama had just been elected to his first statewide political office three years earlier. In both cases, their nominations were validated by the endorsements of Democratic luminaries, including Bryan in 1912 and Kerry in 2007. Both men were rewarded by being nominated for Secretary of State.
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Like Humphrey and McGovern, Kerry returned to the U.S. Senate and became a loyal foot soldier for his party's agenda. Like Cass and Bryan, Kerry's fidelity to his party was rewarded by being nominated to the coveted Cabinet position of Secretary of State. Unlike Democrats Davis and Smith, who expressed open hostility toward their Party's Democratic President, Kerry became a steadfast supporter of the next Democratic President and is now reaping his political reward for that act of loyalty.