I spoke with a half-dozen GOP House and Senate offices today, including those of lawmakers who support the Syria resolution and those who remain undecided. Although phrased differently, the response that I got from all of them was best summed up by one aide to an undecided Senate Republican: “The president is making this very, very hard to support for a lot of members on both sides.”

Secretary of State John Kerry Secretary of State John Kerry (Evan Vucci/Associated Press)

President Obama’s vaunted PR blitz isn’t getting rave reviews. And this isn’t merely because of Secretary of State John Kerry’s unhelpful remark that the strike would be “unbelievably small.” (Most House advisers I spoke with agreed that comment wasn’t “helpful,” but with members not all back in town, it is hard to gauge how much damage it might cause.) Rather, Republicans simply don’t think Obama carries much weight with voters. A House aide to a member leaning toward approval of the resolution told me, “The president has far more faith in the power of his speeches than I do.”

Ironically, the president seems to be doing better in private settings. A person familiar with the meeting of a group of Senate Republicans with Vice President Biden, at which Obama appeared, had this take: “The president made a strong case and his presence was constructive, but it remains to be seen if members will ultimately be persuaded. Still some lingering questions.” As for the PR blitz, he said it doesn’t appear “they have their act together,” citing Kerry’s gaffe.

What accounts for the gap between private and public pitches? One explanation may be that Obama is better able in private to make a more nuanced and compelling case regarding military capabilities and/or conversations and quiet commitments with other global leaders. (We do know that Qatar and Saudi Arabia have voiced support for U.S. action.) However, it’s hard for him to persuade the public and turn the media perception (which is overwhelmingly negative on prospects for passage of the resolution) when all he can do is openly recite rote talking points.

The window of time to persuade lawmakers is closing fast. There are still about 50 undecided senators and more than 200 undecided House members. What the president must do is make the most comprehensive argument possible to members, providing enough public cover and a compelling rationale in public that lawmakers feel obliged to support U.S. action. For that to happen, Obama can’t afford any more unforced errors like today’s “unbelievably” unhelpful Kerry remark.