The New York Times reports:

After another private meeting Monday night with Senator Mitch McConnell of Kentucky, the majority leader, Mr. Trump began complaining privately that he did not think Senate Republicans were doing enough to have his back. For days, some allies of the president’s eldest son, Donald Trump Jr., had agitated on Twitter for Mr. Graham to do more to try to counteract Democrats in the House.

One line of pressure has been for Graham, who chairs the Senate Judiciary Committee, to call witnesses in that chamber as a sort of counterprogramming, though on Thursday he said that made no sense to him.

David A. Graham: Nothing and everything changed on impeachment

But Graham is not the problem; he’s signaled a willingness to stand by Trump through thick, thin, and horrific lynching analogies. The White House’s challenge is other senators. Some Republicans have been notably open to an impeachment inquiry, but most have been conspicuously quiet. Some use the time-honored excuse that they’d serve as jurors in a trial and therefore ought not to weigh in; many more are simply dodging questions. What they’re mostly not doing is mounting substantive defenses of the president’s behavior. A Daily Caller canvass found only seven of the 53 Republicans were willing to rule out voting to remove Trump.

Republican senators have always been less tractable for Trump than representatives, though the GOP controls the Senate but not the House. The president has many rah-rah fans in the House, and House members are also more vulnerable to pressure from Trump-loving constituents if they get out of line with the White House. (Francis Rooney of Florida, the most outspoken Trump critic on the Ukraine matter in recent weeks, has announced he’s retiring.) Senators are more insulated from immediate political pressure, more rooted in Washington and the party structure, and less fond of the president.

Nonetheless, it would take a major change in the evidence against Trump, or a vast shift in polling, for enough Republican senators to support conviction that the president would be in serious danger of removal in a Senate trial. Yet it’s clear that Trump does care a great deal about senators’ positions. The impetus for his hasty cancellation of plans to host the Group of Seven summit at this resort in Doral, Florida, was apparently the anger it provoked among Republican senators. In the past, Trump has been content to weather their displeasure, but this time he folded.

David A. Graham: ‘Get over it’ is the Trump Doctrine

Perhaps Trump believes that a unified GOP Senate response will persuade Democrats not to vote to impeach; I am skeptical that will work. Or perhaps Trump worries about the political damage if a majority of the Senate voted to convict, even if it didn’t lead to removal. It would take only four GOP defections to reach a majority for conviction in the Senate.