WASHINGTON—The Republican-led Senate acquitted President Trump of charges stemming from his efforts to press Ukraine to announce investigations that would benefit him politically, bringing to a close a bruising four-month battle fought almost entirely along party lines.

The third presidential impeachment in U.S. history intensified the nation’s sharp divide over Mr. Trump and previewed many of the arguments likely to be heard ahead of the election this fall. During the trial, Democrats said the Republican president was trying...