Democrats made this mistake in 1972 when they ran the (by the standards of the day) extremely liberal George McGovern, which resulted in Nixon getting re-elected in a 49 state landslide.
Democrats repeated this mistake in 1984 when they ran the (by the standards of the day) extremely liberal Walter Mondale, which resulted in Reagan getting re-elected in a 49 state landslide.
Democrats repeated this mistake in 2004 when they ran the too-liberal John Kerry, which resulted in GWB getting re-elected. OK, that wasn't a landslide by any stretch, but then the incumbent Republican had gotten us into two unwinnable wars during his first term, and by the time of the 2004 election, it was already clear that the invasion of Iraq was initiated under false pretenses.
It starting to seem like Democrats never learn from their mistakes.