Sizable victories for the Democrats in a series of races offer cheer after a year of Donald Trump. But the party should not feel too reassuredIt was the boost they needed. The jubilation of Democrats as they celebrated the results of Tuesday’s elections owed much to the despair of one year before, when they learned that Donald Trump was on his way to the White House, as well as to the extraordinary events since, which have amplified his unfitness for the presidency and the extent of Russia...