With James Mattis out, Patrick Shanahan or Tom Cotton rumored to be potential replacements

With Defense Secretary James Mattis leaving the administration amid deep policy rifts with the commander in chief, President Trump is rumored to be looking inside the Pentagon and to Capitol Hill for a potential replacement.

Neither the White House nor Pentagon would speak on the record Friday about who will take Mr. Mattis’ place, but chatter in the Defense Department and among foreign policy insiders has focused on Deputy Defense Secretary Patrick Shanahan and Sen. Tom Cotton, Arkansas Republican.

Retired Army Gen. Jack Keane, who was previously offered the job at the beginning of Mr. Trump’s tenure, also is believed to be on the president’s short list, but he took himself out of the running late Thursday.

“I don’t intend to go back in the public service. And I’m confident the president will be able to find a capable person to serve the nation,” Mr. Keane, now a national security analyst for Fox News, told NPR shortly after the news of Mr. Mattis’ resignation broke.

With Mr. Mattis set to leave his post at the end of February, the president could tap Mr. Shanahan to serve in an acting role until a permanent replacement is found. A former Boeing executive, Mr. Shanahan has been at the forefront of Mr. Trump’s push to create a “Space Force” as the sixth branch of the military, which could ingratiate him with the president.

Mr. Cotton, the 41-year-old first-year senator from Arkansas, also has long been rumored to be a top candidate for Defense secretary. But Mr. Trump’s stunning decision this week to pull all U.S. troops out of Syria — a policy move that irked Mr. Mattis and sparked his resignation — could change that equation.

Mr. Cotton this week signed on to a bipartisan letter criticizing the president’s decision, arguing it will “embolden” the Islamic State and lead to instability in the region. Sen. Lindsey Graham, South Carolina Republican, also has been rumored to be a candidate.

But like Mr. Cotton, Mr. Graham has been highly critical of the president’s recent foreign policy moves.

Mr. Mattis’ resignation shocked Washington on Thursday night and whoever replaces him is likely to be more aligned with a president who now seems bent on removing U.S. troops from Syria, drawing down the number of forces in Afghanistan, and taking other steps unpopular in military circles and on Capitol Hill.

Mr. Trump’s eventual pick must be confirmed by the Senate, which will still be controlled by Republicans in the new Congress.