text:  Of course, these are national numbers. Some cities have seen increases. Others have seen decreases. Dallas was offered as an example last night. That city has seen declining crime for the last few years. And the city's mayor, Eric Johnson, a former Democrat who switched parties last year while in office, was quick to take credit for that. But I spoke to Ernesto Lopez. He's a researcher at the Council on Criminal Justice about this. He cautioned against trying to pin rising or falling crime rates on any one political party.