michael dimock, what is driving this change? it's unargueble that there's a change going on, but why? >> it's one of the biggest changes we've mean? the last decade and it's driven by two things: the arrival of a new generation that now makes up over 25% of adults in this country, millennials, who are very supportive of this and their support is growing more intense as time passes. but you're finding a lot oaf people of all ages who have changed their minds on this over time. that about a third of supporters say they themselves have shifted in tat direion as time has passed. >> ifill: greg lewis, do you determine it's a political shift cultural shift? knee other or both? >> i would say it's all of those things. we've seen very dramatic 20-point rises in support for same-sex marriage over the past decade. we've been seeing increases of that size on a variety of gay rights issues sort of lagged over the past 30 years. >> ifill: michael dimock said it was about young people changing their min and people gtting more exposed to other