"Harris, characteristically, has made a lawyerly assessment of pros and cons. She and her advisers have queried whether, given the limited number of ATACMS available..."

"... they might be more useful striking Russian targets in occupied Crimea — especially given intelligence reports that Russia has pulled its aircraft that target Ukraine back to bases beyond the missiles’ 300-kilometer range. Another concern for the Harris team is whether the Russians might retaliate by giving long-range missiles to adversaries, such as the Houthis in Yemen, further threatening Red Sea shipping and perhaps Israel.... Lawyers have played a decisive role in national security policy — from Dean Acheson to Jake Sullivan. Harris would sustain that long line of lawyerly balancers and trimmers who weigh risks and benefits before they take action. She might turn a page in our domestic life, but not so much in foreign policy."

Writes David Ignatius, in "These people have seen Harris in the Situation Room. Here’s what they have to say. Harris is 'more hard-line than most people think,' says a retired four-star general who has briefed her many times" (WaPo)(free-access link).

Ignatius assumes we understand what "trimmers" are — "lawyerly balancers and trimmers." There are a lot of meanings to the word "trim," including distracting slang usages (see Urban Dictionary). But, relying on the OED, I've got to choose the nautical meaning: "To distribute the load of (a ship or boat) so that it floats on an even keel." There's also: "To adjust (the sails or yards) with reference to the direction of the wind and the course of the ship, so as to obtain the greatest advantage." But the load distribution metaphor is the one that has been used in politics. The OED has a separate entry for "trimmer," and meaning #5 is expressly political: 

One who trims between opposing parties in politics, etc.; hence, one who inclines to each of two opposite sides as interest dictates. Applied originally in this sense to Lord Halifax and those associated with him (1680–90), but by him accepted in the sense ‘one who keeps even the ship of state’; hence ‘one who changes sides to balance parties’ (Johnson).

Let's find out more about Lord Halifax (Wikipedia):

His intellectual powers, his high character, his urbanity, vivacity and satirical humour made a great impression on his contemporaries, and many of his witty sayings have been recorded. Maintaining throughout his career a detachment from party, he never acted permanently or continuously with either of the two great factions, and exasperated both in turn by deserting their cause at the moment when their hopes seemed on the point of realisation. To them he appeared weak, inconstant, untrustworthy. But the principle which chiefly influenced his political action, that of compromise, differed essentially from those of both parties, and his attitude with regard to the Whigs or Tories was thus by necessity continually changing. Thus the regency scheme, which Halifax had supported while Charles still reigned, was opposed by him with perfect consistency at the revolution. He readily accepted for himself the character of a "trimmer," desiring, he said, to keep the boat steady, while others attempted to weigh it down perilously on one side or the other; and he concluded his tract with these assertions: "that our climate is a Trimmer between that part of the world where men are roasted and the other where they are frozen; that our Church is a Trimmer between the frenzy of fanatic visions and the lethargic ignorance of Popish dreams; that our laws are Trimmers between the excesses of unbounded power and the extravagance of liberty not enough restrained; that true virtue hath ever been thought a Trimmer, and to have its dwelling in the middle between two extremes; that even God Almighty Himself is divided between His two great attributes, His Mercy and His Justice. In such company, our Trimmer is not ashamed of his name. . . ."