Perhaps they are most impactful when he is not announcing anything he will or can do – but when he simply talks about his own views and evolution in a compelling and persuasive way. He can capture and accelerate the evolution of others. And it appears he has:
Of the 53 percent of Americans who say the freedom to marry should be legal, 39 percent voiced that they were “strongly” in support. In contrast, only 32 percent voiced “strong” opposition.
That's a shift, as if an authority figure is sometimes necessary to allow people to own their feelings on an issue which had long been regarded as toxic. The gender gap also evaporates in this latest poll, as if Obama gave some straight men permission to support equality. But notice how this has isolated Republicans even further on this issue (the WaPo interactive tool is awesome, btw):
As the country as a whole grows more supportive of gay equality, the GOP is headed in the other direction. Republican support for marriage equality has declined a full ten points just this year – a pretty stunning result. Have they changed their mind simply because Obama supports something? In today's polarized, partisan climate, I wouldn't be surprised.