With acting cabinet secretaries everywhere, the Departments of Homeland Security and State hollowed out, and the recent departure of high-profile, nonpolitical appointees on the National Security Council staff (the Vindman brothers and Victoria Coates), the judgment and experience about who wants to attack us and where is basically gone. This creates an enormous risk to our country.

While our intelligence community is the most impressive in the world, we can’t see and know everything. No nation can. So we rely on other intelligence services. And not just the ones of Australia, Britain, Canada and New Zealand that, along with the United States, make up the “Five Eyes” intelligence alliance. We also need allies with eyes and ears in places we just can’t go, like North Korea and China. A purge of our best and brightest intelligence officers will signal to them that new management is coming, and current relationships aren’t useful any longer.

Allied services also won’t trust us if our own officers face constant pressure to politicize intelligence. That means reporting streams will dry up, we won’t get early warning on planned attacks and we will lose critical knowledge about the decisions adversaries are making that may not have consequences today, but could have huge ones in the next decade. It’s impossible to know how many clues we will miss if our intelligence community is isolated from the world and the president’s daily brief only reinforces what the administration wants to hear.

A so-called house clearing could damage our intelligence abilities for at least a generation. Recruitment and retention will of course plummet, and those officers and analysts left won’t have the mentorship or the experience to ensure our assessments are based on truth.

For the sake of our country, I hope Mr. Grenell makes a careful assessment of the intelligence community’s capacities and impressive work force before making further changes. How dangerous it would be if we lose the tip of the spear against those who would destroy us.

Jane Harman, a Democrat, represented California in the House from 1993 to 1999 and from 2001 to 2013.

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