This skeptic remains unconvinced.
That's because the members of the Freedom and Justice Party (FJP) - who appeared at a Carnegie Endowment conference on "Islamists in Power" - were promoting more moderate views than those of their leaders in Cairo.
So whom should we believe?
On the role of Islam in government, Abdul Mawgoud Dardery, an eloquent member of Parliament from Luxor, was insistent: "We never thought of our system as divine. We believe in a civil system with Islamic reference."
No clerics in government, he said. And if voters ousted his party next time, he said it would willingly step down.
And what role would sharia law play in an FJP government? I asked.
Dardery said his party would keep Article II of the current constitution, which cites sharia [Islamic jurisprudence] as the main reference for parliamentary laws. This is a vague formulation.
More hardline Salafi Islamists, who won 27 percent of the vote, had demanded that sharia rulings be inserted wholesale into the new constitution. The Brotherhood refused.
But the real tricky question is: Who will decide if parliamentary laws comply with sharia? "Parliament has the final say," Dardery said. "We don't believe in theocracy."
Sounds very European.
Yet back in Cairo, the Egyptian press reports that the Muslim Brotherhood's candidate for president, Khairat el-Shater, told hardline Salafi clerics he would set up a group of religious scholars to "help parliament" achieve compliance with sharia.
If true, this idea sounds just like a proposal the Brotherhood made in 2007, when it was a banned opposition movement.
Brotherhood leaders told me last year this controversial idea wouldn't be resurrected. Yet here it comes again. Moreover, el-Shater reportedly told the clerics that sharia was his ultimate objective. Clearly, he's trying to woo votes away from the Salafi candiate Hafez Abu Ismail.
Then there is the question of the Islamists' openness to pluralism. To prove its commitment to consensus, the Brotherhood originally pledged to contest fewer than 50 percent of parliamentary seats, and not to run a candidate in presidential elections. It soon reneged on both pledges.
The Brotherhood also stressed the need for consensus in writing a new constitution. But when it came to appointing an assembly to write the document, the Brotherhood-dominated parliament chose Islamists to fill 65 of 100 slots. Only five slots went to Christians and six to women.
This disparity has already caused 25 non-Islamist members of the assembly, including Copts, to walk out.
Dardery said the Brotherhood considers Copts as "full citizens." The elegant, white-veiled Sondos Asem, senior editor of the FJP's official website, insisted that the party "seeks to improve the situation of women in society."
Yet the FJP ran women so low on its parliamentary lists that almost none were elected. Dardery seemed taken aback when I said that many Egyptian Christians, and educated women are terribly frightened for their future under an Islamist government.
Indeed, I think Brotherhood members are so convinced of their righteousness they may not realize how much it frightens everyone else.
However, the fact that the Egyptian Brotherhood sees the need to conduct a charm offensive indicates it knows the world is watching. Islamists know they need that world to invest in Egypt's sinking economy.
That provides leverage for Western governments to press for pluralism, and adherence to Egypt's peace treaty with Israel. (The FJP delegation said all international obligations would be respected, but back in Cairo I've heard senior Brothers say the treaty might be put to a vote.)
In the end, what will matter is not what FJP members say in Washington, but what positions their leaders take back in Cairo. In other words, watch what they do, not what they say.
E-mail Trudy Rubin