Here's a scenario in which the 2012 vote is split between HRC, Trump, the GOP nominee, and other candidates as follows:
Obama 2012 vote --> 90% goes to HRC, 10% goes to Trump
Romney 2012 vote --> 40% goes to Trump, 70% goes to the GOP nominee (that adds up to more than 110% to simulate Trump turning out new GOP-leaning voters.
Other 2012 vote --> 80% to Trump, 60% to other 2016 (again, more than 100% for similar reasons).
Nationally that gives you HRC 46.0%, Trump 25.4%, GOP Nominee 33.0%, other 1.0%
Then you would want to ideally adjust further based on demographics. For example, Trump will get a larger than average share of the Romney 2012 vote in West Virginia, but a larger than average share of the Romney vote in Connecticut (etc.). But here's the uniform swing without any of those additional adjustments. With this uniform adjustment Trump doesn't win any states, but you can imagine that he would in reality do better in some states than others - he could win states like WV, ID, any of the plains states --- basically anywhere that is heavily GOP, heavily white, and not overly educated. On the other hand, HRC would have a shot at some other states like TX, MT, and some random other ones if the vote split worked out her way.
HRC Trump GOP Other
AL 34.5% 28.9% 42.4% 0.7%
AK 36.7% 29.5% 38.4% 2.6%
AZ 40.1% 27.3% 37.6% 1.1%
AR 33.2% 30.0% 42.4% 1.5%
CA 54.2% 23.0% 26.0% 1.6%
CO 46.3% 25.5% 32.3% 1.4%
CT 52.3% 23.1% 28.5% 0.7%
DE 52.7% 23.0% 28.0% 0.8%
DC 81.8% 13.4% 5.1% 1.1%
FL 45.0% 25.3% 34.4% 0.5%
GA 40.9% 26.8% 37.3% 0.7%
HI 63.5% 19.5% 19.5% 1.0%
ID 29.4% 31.4% 45.2% 1.7%
IL 51.8% 23.4% 28.5% 1.0%
IN 39.5% 27.6% 37.9% 1.2%
IA 46.8% 25.1% 32.3% 1.1%
KS 34.2% 29.5% 41.8% 1.4%
KY 34.0% 29.3% 42.3% 1.0%
LA 36.5% 28.5% 40.4% 1.0%
ME–a/l 50.6% 24.2% 28.7% 1.6%
ME–1 53.6% 23.0% 26.7% 1.4%
ME–2 47.6% 25.2% 31.1% 1.6%
MD 55.8% 22.3% 25.1% 1.3%
MA 54.6% 22.5% 26.3% 1.1%
MI 48.8% 24.2% 31.3% 0.6%
MN 47.4% 25.2% 31.5% 1.4%
MS 39.4% 27.2% 38.7% 0.6%
MO 39.9% 27.4% 37.6% 1.1%
MT 37.5% 28.7% 38.7% 1.8%
NE–a/l 34.2% 29.5% 41.9% 1.3%
NE–1 36.9% 28.3% 40.3% 0.9%
NE–2 41.2% 26.8% 37.1% 0.8%
NE–3 25.2% 32.2% 49.4% 0.9%
NV 47.1% 25.1% 32.0% 1.2%
NH 46.8% 25.1% 32.5% 1.0%
NJ 52.5% 22.9% 28.4% 0.6%
NM 47.7% 25.8% 30.0% 2.5%
NY 57.0% 21.6% 24.6% 0.9%
NC 43.5% 26.0% 35.3% 0.8%
ND 34.8% 29.6% 40.8% 1.8%
OH 45.6% 25.5% 33.4% 1.0%
OK 29.9% 30.0% 46.7% 0.0%
OR 48.8% 25.2% 29.5% 2.2%
PA 46.8% 25.0% 32.6% 0.9%
RI 56.4% 22.0% 24.7% 1.2%
SC 39.7% 27.3% 38.2% 0.8%
SD 35.9% 28.9% 40.5% 1.3%
TN 35.2% 28.9% 41.6% 0.9%
TX 37.2% 28.2% 40.0% 0.9%
UT 22.3% 33.6% 51.0% 1.5%
VT 59.9% 21.0% 21.7% 1.5%
VA 46.0% 25.3% 33.1% 0.9%
WA 50.5% 24.2% 28.9% 1.5%
WV 32.0% 30.2% 43.6% 1.3%
WI 47.5% 24.7% 32.1% 0.8%
WY 25.0% 33.1% 48.0% 2.1%
US 46.0% 25.4% 33.0% 1.0%
