WASHINGTON — In the latest sign of the closer collaboration between the Koch brothers and President Trump, Treasury Secretary Steven Mnuchin and White House aide Marc Short will appear Monday with top leaders of the Kochs' conservative network to promote Trump's tax plan

The high-profile session Monday at the Newseum in Washington comes as the policy and political empire affiliated with billionaire industrialists Charles Koch and his brother David Koch kicks off the grassroots phase of its multimillion-dollar campaign to advance Trump's blueprint to slash the corporate tax rate and enact broader cuts.

Charles Koch, one of the most influential players in Republican politics, did not back Trump's candidacy, but he and the other wealthy donors in his network are throwing their muscle behind the tax overhaul.

On Thursday, GOP tax negotiators on Capitol Hill and the White House announced they had reached a deal on the general principles that would guide their overhaul of the tax code. Koch officials hailed the decision by lawmakers and the administration to exclude a proposed border-adjustment tax, which they said would have led to higher prices on consumer goods.

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Charles Koch expressed reservations about Trump's policies and rhetoric during the 2016 campaign, but he has close ties to key people in the administration, including Vice President Pence.

Short, Trump's director of legislative affairs, is a former top Koch aide.

Mnuchin and Short will appear with Tim Phillips, who runs Americans for Prosperity, the Kochs' grassroots arm, and James Davis, a top network spokesman, according to a news release.