Yes it is a mandate, just take a look at the congress. 4 years ago with Bush running the R's lost about 5 seats each in the House and Senate. Now the R's have gained about 5 seats in each.
BTW here's a list of all-time vote getters
1. Bush 2004
2. Kerry 2004
3. Reagan 1984
4. Gore 2000
5. Bush 2000
6. Bush 1988
7. Clinton 1996
8. Nixon 1972
9. Clinton 1992
10. Reagan 1980
Wow, four of the top five in the past two elections
I think that's more of a testament to how well Reagan did in 1984 than to how well Bush did in 2004.