From the article :

Clinton signaled in July that she was skeptical of the decision, telling a reporter in New Hampshire that she had "doubts about whether we should continue drilling in the Arctic."

"I don't think it is a necessary part of our overall clean energy climate change agenda," Clinton said. "I will be talking about drilling in general but I am skeptical about whether we should give the go ahead to drill in the Arctic."

Tuesday's tweet plants Clinton squarely in the opposed category, and aligns her with environmental activists who want the United States to wean itself off fossil fuels and say drilling in the Arctic will deepen the country's commitment to oil.

However, the time to be against it was before Obama approved it not after the fact.

If she came out loud about it early she may have persuaded the right decision. Monday quarterbacking is easy.