Blaine was appointed to the Senate on July 10, 1876, but did not begin his duties there until the Senate convened in December of that year.
While in the Senate, he served on the Appropriations Committee and held the chairmanship of the Committee on Civil Service and Retrenchment, but he never achieved the role of leadership that he had held as a member of the House.
The Senate in the 45th Congress was controlled by a narrow Republican majority, but it was a majority often divided against itself and against the Hayes administration.
Blaine did not number himself among the administration's defenders, but neither could he join the Republicans led by Conkling—later known as the Stalwarts—who opposed Hayes, because of the deep personal enmity between Blaine and Conkling.
He opposed Hayes's withdrawal of federal troops from Southern capitals, which effectively ended the Reconstruction of the South, but to no avail.
Blaine continued to antagonize Southern Democrats, voting against bills passed in the Democrat-controlled House that would reduce the Army's appropriation and repeal the post-war Enforcement Acts he had helped pass.
Such bills passed Congress several times and Hayes vetoed them several times; ultimately, the Enforcement Acts remained in place, but the funds to enforce them dwindled.
By 1879, there were only 1,155 soldiers stationed in the former Confederacy, and Blaine believed that this small force could never guarantee the civil and political rights of black Southerners—which would mean an end to the Republican party in the South.

On monetary issues, Blaine continued the advocacy for a strong dollar that he had begun as a Representative.
The issue had shifted from debate over greenbacks to debate over which metal should back the dollar: gold and silver, or gold alone.
The Coinage Act of 1873 stopped the coinage of silver for all coins worth a dollar or more, effectively tying the dollar to the value of gold.
As a result, the money supply contracted and the effects of the Panic of 1873 grew worse, making it more expensive for debtors to pay debts they had entered into when currency was less valuable.
Farmers and laborers, especially, clamored for the return of coinage in both metals, believing the increased money supply would restore wages and property values.
Democratic Representative Richard P. Bland of Missouri proposed a bill, which passed the House, that required the United States to coin as much silver as miners could sell the government, thus increasing the money supply and aiding debtors.
In the Senate, William B. Allison, a Republican from Iowa offered an amendment to limit the silver coinage to two to four million dollars per month.
This was still too much for Blaine, and he denounced the bill and the proposed amendment, but the amended Bland–Allison Act passed the Senate by a 48 to 21 vote.
Hayes vetoed the bill, but Congress mustered the two-thirds vote to pass it over his veto.
Even after the Bland–Allison Act's passage, Blaine continued his opposition, making a series of speeches against it during the 1878 congressional campaign season.

His time in the Senate allowed Blaine to develop his foreign policy ideas.
He advocated expansion of the American navy and merchant marine, which had been in decline since the Civil War.
Blaine also bitterly opposed the results of the arbitration with Great Britain over American fishermen's right to fish in Canadian waters, which resulted in a $5.5 million award to Britain.
Blaine's Anglophobia combined with his support of high tariffs.
He had initially opposed a reciprocity treaty with Canada that would have reduced tariffs between the two nations, but by the end of his time in the Senate, he had changed his mind, believing that Americans had more to gain by increasing exports than they would lose by the risk of cheap imports.
Blaine was appointed to the Senate on July 10, 1876, but did not begin his duties there until the Senate convened in December of that year. While in the Senate, he served on the Appropriations Committee and held the chairmanship of the Committee on Civil Service and Retrenchment, but he never achieved the role of leadership that he had held as a member of the House. The Senate in the 45th Congress was controlled by a narrow Republican majority, but it was a majority often divided against itself and against the Hayes administration. Blaine did not number himself among the administration's defenders, but neither could he join the Republicans led by Conkling—later known as the Stalwarts—who opposed Hayes, because of the deep personal enmity between Blaine and Conkling. He opposed Hayes's withdrawal of federal troops from Southern capitals, which effectively ended the Reconstruction of the South, but to no avail. Blaine continued to antagonize Southern Democrats, voting against bills passed in the Democrat-controlled House that would reduce the Army's appropriation and repeal the post-war Enforcement Acts he had helped pass. Such bills passed Congress several times and Hayes vetoed them several times; ultimately, the Enforcement Acts remained in place, but the funds to enforce them dwindled. By 1879, there were only 1,155 soldiers stationed in the former Confederacy, and Blaine believed that this small force could never guarantee the civil and political rights of black Southerners—which would mean an end to the Republican party in the South.
On monetary issues, Blaine continued the advocacy for a strong dollar that he had begun as a Representative. The issue had shifted from debate over greenbacks to debate over which metal should back the dollar: gold and silver, or gold alone. The Coinage Act of 1873 stopped the coinage of silver for all coins worth a dollar or more, effectively tying the dollar to the value of gold. As a result, the money supply contracted and the effects of the Panic of 1873 grew worse, making it more expensive for debtors to pay debts they had entered into when currency was less valuable. Farmers and laborers, especially, clamored for the return of coinage in both metals, believing the increased money supply would restore wages and property values. Democratic Representative Richard P. Bland of Missouri proposed a bill, which passed the House, that required the United States to coin as much silver as miners could sell the government, thus increasing the money supply and aiding debtors. In the Senate, William B. Allison, a Republican from Iowa offered an amendment to limit the silver coinage to two to four million dollars per month. This was still too much for Blaine, and he denounced the bill and the proposed amendment, but the amended Bland–Allison Act passed the Senate by a 48 to 21 vote. Hayes vetoed the bill, but Congress mustered the two-thirds vote to pass it over his veto. Even after the Bland–Allison Act's passage, Blaine continued his opposition, making a series of speeches against it during the 1878 congressional campaign season.
His time in the Senate allowed Blaine to develop his foreign policy ideas. He advocated expansion of the American navy and merchant marine, which had been in decline since the Civil War. Blaine also bitterly opposed the results of the arbitration with Great Britain over American fishermen's right to fish in Canadian waters, which resulted in a $5.5 million award to Britain. Blaine's Anglophobia combined with his support of high tariffs. He had initially opposed a reciprocity treaty with Canada that would have reduced tariffs between the two nations, but by the end of his time in the Senate, he had changed his mind, believing that Americans had more to gain by increasing exports than they would lose by the risk of cheap imports.
James G. Blaine