David Leonhardt: Bernie Sanders is making a big mistake

The last four presidents — Bill Clinton, George W. Bush, Barack Obama and Donald Trump — are four very different politicians. But they have one crucial similarity: They all tried to appeal to voters who weren’t obvious supporters.Clinton promised a “third way,” distinct from traditional Democratic or Republican policies. Bush ran on compassionate conservatism. Obama said that red and blue America shared more in common than pundits claimed.Even Trump, radical as he i