As the leading Democrat on the influential United States House Committee on Ways and Means during the first Grover Cleveland and Benjamin Harrison administrations, Mills advocated for trade liberalization.

Additionally, he was unable to block the enactment of the McKinley Tariff of 1890 after Republicans gained control of the House on a pro-tariff platform.

Later, as a colonel, he commanded the 10th Texas Infantry Regiment at Arkansas Post, Chickamauga (where he led the brigade of Gen. James Deshler during part of the battle), Missionary Ridge and the Atlanta Campaign.

Elsewhere, he was said to have vowed, "A good sluice of pine top whiskey would improve the morals of the Dallas [Prohibition] convention and the average Prohibitionist."

The reporter Frank G. Carpenter described him as true as steel and unpretentious in dress: "He is tall, straight and big chested," he wrote in 1888.

"The distance between the top button of his high vest and the small of his back is longer than the width of the shoulders of the ordinary man, and he has a biceps which, if put into training, would knock down an ox.

"[3] Mills had made the tariff his special study and long been recognized as one of the leading authorities on the Democratic side.

His selection, according to Ida Tarbell, a historian on the tariff, "was a red rag to the high protectionists, for Mr. Mills was an out-and-out free trader.

[5] He requested for Congress to pass a drastic reduction of the tariff on many manufactured goods to promote trade and reduce the cost of living for ordinary citizens.

[6] Indeed, Chairman Mills, using the Walker Tariff of 1846 as a guideline, had been drafting a bill since September 1887 that would address several of the proposals included by Cleveland in his December message.

The bill provided for a reduction of the duties on sugar, earthenware, glassware, plate glass, woolen goods and other articles; the substitution of ad valorem for specific duties in many cases; and the placing of lumber (of certain kinds), hemp, wool, flax, borax, tin plates, salt and other articles on the free list.

[14] Mills was elected to the US Senate from Texas in 1892 to fill the vacant seat of John H. Reagan and continued to serve in that post until 1899.

In 1893, when President Grover Cleveland sought repeal of the Sherman Silver Purchase Act, Mills gave loyal support.

Today he made one of the most extreme and wild jingo speeches in the Senate on the Cuban question that has marked the whole debate.