Smith says their common ancestor had two wives, one Democrat and one Republican — and the great-grandmothers' party ties carry on. "Their branch was Democratic, and my branch was on the other side," he says.
Despite that, "My relationship with (Mark and Tom) in the Senate would be warm and brotherly, just as it is now," he adds. "We've got equal amounts of Udall in all of us."
After growing up together in Tucson, "we're more like brothers than cousins," Tom Udall says of Mark. "We share ideas in terms of what the challenges are and how to deal with them."
Despite his popularity and an early "Draft Udall" movement by supporters, Tom Udall delayed entering the Senate race until New Mexico Gov. Bill Richardson confirmed he would not run if his presidential bid faltered.
Mark Udall calls Tom a "mentor to me and a very good friend. I'm excited he's in. But we'll have to run each (of) our own races."
Before politics, both worked for the Outward Bound wilderness school. In May, they scaled 14,047-foot Culebra Peak in Colorado — completing Mark Udall's goal of climbing all 53 of the state's 14,000-foot mountains.