Special counsel Robert Mueller's report poses a test for vulnerable Senate Republicans running for reelection, forcing them to decide how far to distance themselves from President Trump heading into 2020. Mueller declined to pursue charges of conspiracy, illegal coordination or obstruction of justice, but much of his report reflects poorly on the president and reveals there are several more federal investigations that have yet to wrap up. While House Democrats will need to decide how hard to go to attack Trump in the wake of the report and whether to pursue a politically charged impeachment process, Senate Republicans have to...