What it says on the tin.
I will vote yes on both questions, based on the following assumptions:
Humphrey, as a member of the administration that escalated the war, and seeking the domestic cooperation of increasingly dissatisfied Democrats, will be under internal partisan and constituent pressure to terminate US involvement in the war faster.
In addition to removing US troops faster, and making it politically easier for Congress to cut aid once US troops are out, he is likely to inflict less damage on VC infrastructure and VC and VC and NVA sanctuaries and interdict fewer North Vietnamese logistic routes while conducting withdrawal.
Vietnamization will also be more rushed so Saigon's spread of control will be even more tenuous than it was in OTL.
When US troops and advisors withdraw, almost certainly before 1970 or 1971 is out, the combat and leadership contribution goes, and possibly even more important, their oversight of US aid to ARVN.
Meanwhile further rapid domestic turmoil and change, increasingly left-liberal Supreme Court decisions, and humiliation overseas, will prime conservative Republicans to coalesce around Reagan and win the general in 1972.