Republican activists in early voting states like Iowa and New Hampshire generally speak of Sarah Palin’s presidential prospects in encouraging terms. She’s a star, they say. If she decides to run, she’ll shake up the field. Lately, the praise has been tempered with warnings about how her time is growing short. But on Monday, the day Palin appeared before a large and very enthusiastic crowd at a Tea Party Express rally here, and two days after her much-anticipated speech to the Tea Party of America in Indianola, Iowa, a plugged-in New Hampshire Republican said he believes her window has already...