In sizing up the 2016 election, some on the left are concerned that Bernie Sanders' presence in the Democratic ranks could work to that party's detriment. Count former Rep. Barney Frank among them.

Frank, who retired from his 32-year stint as a Massachusetts congressman in 2013, expressed as much in an op-ed featuring the blunt headline, "Why Progressives Shouldn't Support Bernie," published in Politico on Thursday:

Of course Republicans recognize that at its most vigorous, a debate between Clinton and Sanders on how — not whether — to toughen financial regulation or diminish income inequality will fall decibels short of the fundamental arguments between Ted Cruz and Jeb Bush on immigration, Lindsey Graham and Rand Paul on military intervention, Ben Carson and Mike Huckabee against many others on how sharply to press against same-sex marriage, and Donald Trump and all of the others on the role of rational discussion in politics. But they believe boosting Sanders' candidacy is their only way to prevent [Hillary] Clinton emerging as the nominee with broad support early in the process, strengthening her position in November.