According to The Guardian, the Conference really did happen over a three-day period in DC.
https://www.theguardian.com/us-news/2025/sep/06/national-convservatism-conference-trumphttps://www.theguardian.com/us-news/2025/sep/06/national-convservatism-conference-trump
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These WashPost articles may be behind a paywall but they describe the conference:
https://www.washingtonpost.com/politics/2025/09/06/maga-britain-migration-trump-muslim/https://www.washingtonpost.com/politics/2025/09/06/maga-britain-migration-trump-muslim/
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https://www.washingtonpost.com/politics/2025/09/05/national-conservativism-conference-schmitt/6114586c-8a85-11f0-895c-97bd39cbdc59_story.htmlhttps://www.washingtonpost.com/politics/2025/09/05/national-conservativism-conference-schmitt/6114586c-8a85-11f0-895c-97bd39cbdc59_story.html
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The second Post article does describe a conference hall as "half-full", however, the speakers' list was extensive.
Here are some excerpts from the Post article.
Members of Congress, Trump administration officials, donors and right-wing pundits gathered this week for the annual National Conservatism Conference a gathering once seen as fringe, now asserting itself as the GOPs dominant ideological force. Panel titles ranged from The Threat of Islamism in America to The Bible and American Renewal to Overturn Obergefell, the Supreme Court case that legalized same-sex marriage .
. . .
This years conference was held in the heart of Washington, just blocks from the White House.
. . .
High-profile speakers included Director of National Intelligence Tulsi Gabbard , White House budget director Russell Vought , Trump border czar Tom Homan , and three U.S. senators. The speaker list also featured more controversial figures, such as John Eastman an ex-Trump attorney central in efforts to overturn the 2020 election after Trumps loss to Democrat Joe Biden and Calvin Robinson , a Michigan priest who lost his license after mimicking a straight-arm gesture interpreted by some as a Nazi salute.