Although sales of existing and newly constructed homes were both up in January 2017, a slump in the number of contracts signed for existing homes may be a harbinger of a rough spring market. A low supply of homes on the market, especially in the Midwest and West, caused a lull in pending home sales at the beginning of the year, according to a National Association of Realtor index based on contract signings. The Pending Home Sales Index showed that the number of homes with a contract in January was the lowest it’s been since January 2016. Existing home sale gains (up 3.3 percent in January) showed...