Miller reportedly played a central role in the resignation in April 2019 of Secretary of Homeland Security Kirstjen Nielsen, whom he believed was insufficiently hawkish on immigration.

As a White House spokesman, Miller on multiple occasions made false and unsubstantiated claims regarding widespread electoral fraud.

Emails leaked in November 2019 showed that Miller had promoted articles from white nationalist publications VDARE and American Renaissance, and had espoused conspiracy theories.

[9] Miller's uncle recalls that, when Wolf-Lieb Glosser reached Ellis Island on January 7, 1903 with $8 to his name, "[t]hough fluent in Polish, Russian and Yiddish, he understood no English.

[15] Miller invited conservative activist David Horowitz to speak, first at the high school and later at Duke University; afterward he denounced the fact that neither institution would authorize the event.

[11] Miller was in the habit of "riling up his fellow [high school] classmates with controversial statements";[16] for instance, he told Latino students to speak only English.

[15] David Horowitz, whom the Southern Poverty Law Center describes as an anti-Muslim, anti-immigrant extremist, published an essay by Miller, "How I Changed My Left-Wing High School", on his website.

History professor KC Johnson described Duke's atmosphere during the case as not "conducive to speaking up" and praised Miller's role in it: "I think it did take a lot of courage, and he has to get credit for that.

[26] After graduating from college, Miller began to work as a press secretary for Congresswoman Michele Bachmann, a Tea Party Republican, after David Horowitz connected them.

[29] Miller was seen as sharing an "ideological kinship" with former White House chief strategist and Breitbart News co-founder Steve Bannon, and had a "long collaboration" with him.

[49] In September 2017, The New York Times reported that Miller stopped the Trump administration from showing the public an internal study by the Department of Health and Human Services that found that refugees had a net positive effect on government revenues.

[54] The New York Times had also reported in November 2017 that Miller was in regular contact with George Papadopoulos during the campaign about his discussions with Russian government officials.

[55] Miller and Sessions were described as the chief champions of the Trump administration's decision to start to separate migrant children from their parents when they crossed the U.S.

[57] In July 2018, senior White House official Jennifer Arangio was fired after she reportedly advocated that the United States remain in the Global Compact for Migration (a United Nations plan intended to "cover all dimensions of international migration in a holistic and comprehensive manner"[58]), defended the State Department's refugee bureau when Miller sought to defund it, and corrected misleading information about refugees that Miller was presenting to Trump.

[59][60] "I have watched with dismay and increasing horror as my nephew, an educated man who is well aware of his heritage, has become the architect of immigration policies that repudiate the very foundation of our family's life in this country."

[62] According to Chaos Under Heaven, a book by Josh Rogin, Miller was part of a group of officials that wanted Trump to "speed the downfall" of the Chinese Communist Party and that "believed in economic nationalism, the return of manufacturing from abroad, and the protection of domestic industries, even at the expense of free trade".

Miller argued that a ban was necessary to reduce Chinese espionage, but that another benefit was that it would hurt elite universities with staff and students critical of Trump.

[68] Miller reportedly played a central role in Secretary of Homeland Security Kirstjen Nielsen's resignation on April 7, 2019, as part of a larger department overhaul[69] aimed at steering the Trump administration towards a "tougher" approach on immigration.

[70] Nielsen had opposed a plan Miller supported whereby the Trump administration would carry out mass arrests of undocumented immigrant families in 10 major U.S.

[71] Quartz reported that Miller had been purposely leaking information on border apprehensions and asylum seekers to the Washington Examiner so that the paper would publish alarming anti-immigration stories that criticized Nielsen.

[74] Following the exposé by the Southern Poverty Law Center in November 2019, Omar reshared the April tweet in which she had called Miller a white nationalist, adding that "now we have the emails to prove it".

[81] According to The New York Times, in the spring of 2020, Miller requested that the Department of Homeland Security develop a plan to use American troops to seal the entire U.S. border with Mexico.

Government officials estimated that such a plan would require the deployment of approximately 250,000 troops, or more than half of the active army, constituting the largest use of American military force within the country since the Civil War.

[82] During the 2020 election, Miller said that if Trump were reelected, the administration would seek to limit asylum, target sanctuary city policies, expand the "travel ban" and cut work visas.

[84] After Trump lost the 2020 election and failed to get the result overturned in courts or state legislatures, on December 14, Miller described on television a plan to send "alternate" slates of electors to Congress.

[92][93][94][95] In response to the exposé, White House press secretary Stephanie Grisham called the SPLC an "utterly discredited, long-debunked far-left smear organization.

[109] In February 2025, Miller and Peter Navarro were leading officials in the economic discussions regarding the imposition of tariffs on Canada, China and Mexico.

[110] On February 8, 2016, Miller participated in an interview with InfoWars, during which he praised the site and its owner, Alex Jones, for its coverage of immigration and the Trans-Pacific Partnership.

"[112][113] Miller's assertion was met with criticism from legal experts, such as Ilya Shapiro of the Cato Institute (who said that the administration's comments could undercut public confidence in the judiciary) and Cornell Law School professor Jens David Ohlin (who said that the statement showed "an absurd lack of appreciation for the separation of powers" set forth in the Constitution).

In the course of the interview, Miller called Steve Bannon's comments about the Trump Tower meeting in Michael Wolff's book Fire and Fury "grotesque".