He may also have suspected that such intervention would not have been enough to save Ames. Looking at Tilden's winning margin in MS, that assumption was probably correct.
A curious thing is that although Tilden's victory in Mississippi in 1876 is supposed to have been caused by suppression of the African American vote, there were considerably more votes cast in the state in 1876 than in 1872.
http://psephos.adam-carr.net/countries/u/usa/pres/1872.txt
http://psephos.adam-carr.net/countries/u/usa/pres/1876.txt Did some whites who abstained in 1872 vote in 1876? (Clearly a number who had voted Republican in 1872 switched to the Democrats.) Were some blacks intimidated not into not-voting but voting for the Democrats? (David Donald has written of the 1875 election that "In some five delta counties, moreover, the Democratic vote was so large as to justify the belief that wealthy landowners 'voted' their colored tenants for the Democratic party." https://books.google.com/books?id=__OQ__dLw-MC&pg=PA274)