President Trump, supposedly a woman-abuser, showed greater respect for Barbara Bush than his critics would have anticipated, since the U.S. Code doesen't even recognize the First Ladies who sacrifice so much and take so much heartache for the sake of the institution of family in these U.S. That is a deficiency in the Code, IMHO.
McCain got what he deserved according to the law as written; then the rest was political pressure from the same media that hated McCain when he ran for President. Had McCain done the right thing and retired from Congress when he learned his condition was terminal instead of his usual betrayal of his constituents and bitter and suspect manipulations, he might have fallen under the "other officials" or "principal figures" discretion of the law instead of the specific instruction for "a Member of Congress."
U.S. Code § 7 - Position and manner of display
(m)...By order of the President, the flag shall be flown at half-staff upon the death of principal figures of the United States Government and the Governor of a State, territory, or possession, as a mark of respect to their memory. ...
...In the event of the death of other officials or foreign dignitaries, the flag is to be displayed at half-staff according to Presidential instructions or orders, or in accordance with recognized customs or practices not inconsistent with law. ...
The flag shall be flown at half-staff 30 days from the death of the President or a former President; 10 days from the day of death of the Vice President, the Chief Justice or a retired Chief Justice of the United States, or the Speaker of the House of Representatives; from the day of death until interment of an Associate Justice of the Supreme Court, a Secretary of an executive or military department, a former Vice President, or the Governor of a State, territory, or possession; and on the day of death and the following day for a Member of Congress.
Would conservatives be giving Hillary this kind of latitude had the death been Jim Jordan and she only gave him protocol respect?