The mayor of deep blue Dallas has ditched the Democratic Party, citing his disdain for 'virtue signaling.' It gives the GOP a foothold in one of America's biggest cities.

• Eric Johnson, the mayor of Dallas, has left the Democratic Party and joined the GOP.
• Johnson, in a WSJ op-ed, called out Democrats for what he said was their "virtue signaling" on issues.
• The party switch gives Republicans a major foothold in one of the country's most populous cities.

For years, Republicans have struggled to win over voters in America's largest cities, in part because of the dominance of the party's conservative wing.

But on Friday, Dallas Mayor Eric Johnson switched from the Democratic Party to the GOP, giving the party a major foothold in the ninth-largest city in the country — and perhaps aiding Republicans in a state where they still dominate but are battling back a fierce resistance from the state's Democrats.