Since The White House is not in the practice of publishing who the President talks to and what they discuss, we can only speculate at this point, but there are some likely possibilities.
The Daily Beast reported that Trump adviser Matt Schlapp has been working as a lobbyist on behalf of a Rhode Island casino that would compete with the new casino, if it was approved:
At least two Trump-connected firms were hired this year to lobby on behalf of Twin River Management Group, which owns a casino in Rhode Island that would directly compete with one planned by the Mashpee Wampanoag. The tribe needs Congress to enshrine its tribal rights in order to rescue the troubled casino deal in nearby Taunton, Massachusetts.
One of those those firms is run by Trump adviser Matt Schlapp, who has, since January, been lobbying Congress and the White House. Twin River has paid his firm, Cove Strategies, $30,000 for its work so far this year.
Schlapp, who is also the husband of White House strategic communications director Mercedes Schlapp, has publicly criticized legislation to recognize the tribe and he too has done so by invoking Warren.
Supporting evidence for this link is the fact that Schlapp tweeted about this bill just an hour before Trump's tweet, using very similar language that tied the bill to Elizabeth Warren:
And soon full House will vote to reward Sen Elizabeth Warren with...wait for it...an INDIAN casino in Massachusetts.
Of course, there's no way to know if this is a coincidence, the result of active lobbying by Schlapp, or if Trump just saw the tweet and copied it.
In an Analysis piece, The Washington Post cites the Daily Beast story, but also suggests some other possibilities, including:
- other Republicans who opposed the bill:
Rep. Gary Palmer (R-Ala.) [who] was reportedly among those fighting the legislation behind closed doors Tuesday night
- Conservative media outlets like the Free Beacon, who are attracted by the Warren connection:
Conservative media outlets have drawn attention to the bill and to Warren’s association with it
- and Trump's previous opposition to Indian Casinos:
Trump testified before Congress in 1993 and questioned whether the Native Americans building casinos were actually Native Americans. “They don’t look like Indians to me,” he said. “They don’t look like Indians to Indians.”