Several candidates can't beat him when the votes are split and there are winner take all states. Hillary Clinton had 0 events in Wisconsin and very few events in Michigan, while Obama visited both many times in 2008. She spent 15 days of September in New York. She only had 2 battleground state events in Nevada and Ohio in the last half of August.
This was Clinton's schedule in late August:
http://www.p2016.org/clinton/clintoncal0816.html
August 18 - New York, NY
August 19 - Martha's Vineyard, MA
August 20 - Nantucket, MA, Martha's Vineyard, MA
August 21 - Provincetown, MA, Osterville, MA
August 22 - Beverly Hills, CA
August 23 - Los Angeles, CA, Laguna Beach, CA, Piedmont, CA
August 24 - Redwood City, CA, Los Altos, CA, Woodside, CA
August 25 - Reno, NV
August 26 - None
August 27 - White Plains, NY
August 28 - Sag Harbor, NY, Southampton, NY, Bridgehampton, NY
August 29 - East Hampton, NY, Quogue, NY
August 30 - Sagaponack, NY, North Haven, NY
August 31 - Cincinnati, OH
http://www.p2016.org/clinton/clintoncal0916.html
1 Ohio event, 0 Michigan events, 1 Pennsylvania event, 0 Wisconsin events,
15-16 days in New York
September 1 - None
September 2 - None
September 3 - None
September 4 - None
September 5 - Cleveland, OH, Hampton, IL
September 6 - Tampa, FL
September 7 - New York, NY
September 8 - Charlotte, NC, Kansas City, MO
September 9 - New York, NY
September 10 - None
September 11 - New York, NY, Chappaqua, NY
September 12 - Chappaqua, NY
September 13 - Chappaqua, NY
September 14 - Chappaqua, NY
September 15 - Greensboro, NC, Washington, DC
September 16 - Washington, DC, New York, NY
September 17 - Washington, DC
September 18 - None
September 19 - Philadelphia, PA, New York, NY
September 20 - None
September 21 - Orlando, FL
September 22 - Chappaqua, NY
September 23 - Rye Brook, NY
September 24 - Rye Brook, NY
September 25 - New York, NY, Rye Brook, NY
September 26 - Hempstead, NY
September 27 - Raleigh, NC
September 28 - Durham, NH, Boston, MA
September 29 - Des Moines, IA, Chicago, IL
September 30 - Fort Pierce, FL, Coral Springs, FL, Miami Beach, FL