In 1834 married Miss Jane Means Appleton, daughter of Rev. Jesse Appleton, president of Bowdoin College.  In 1837 was elected to the United States Senate.  On account of ill health of his wife, deeming it best for her to return to New Hampshire, on June 28, 1842, resigned his seat, and returning to his home resumed the practice of the law.  In 1838 he changed his residence from Hillsboro to Concord.  In 1845 declined an appointment to the United States Senate to fill a vacancy.  Also declined the nomination for governor, tendered by the Democratic State convention, and in 1845 an appointment to the office of Attorney-General of the United States, tendered by President Polk.  In 1846, when the war with Mexico began, he enlisted as a private in a volunteer company organized at Concord; was soon afterwards commissioned colonel of the Ninth Regiment of Infantry; March 3, 1847, was commissioned brigadier-general in the Volunteer Army, and on March 27 embarked for Mexico, arriving at Vera Cruz June 28.  August 6, 1847, joined General Scott with his brigade at Puebla, and soon set out for the capture of the City of Mexico.  Took part in the battle of Contreras September 19, 1847, in which engagement he was severely injured by being thrown from his horse.  The next day, not having recovered, he undertook to accompany his brigade in action against the enemy, when he fainted.  He persisted in remaining on duty in the subsequent operations of the Army.  His conduct and services were spoken of in high terms by his superior officers, Generals Scott, Worth, and Pillow.  Before the battle of Molino del Rey was appointed one of the American commissioners in the effort for peace, a truce being declared for that purpose.  The effort failed and the fighting was renewed.  Participated in the battle of Molino del Rey and continued on duty till peace was declared.  Resigned his commission in March, 1848, and returned to his home.  The same month the legislature of his State voted him a sword of honor in appreciation of his services in the war.  Resumed his law practice and was highly successful.  In 1850 was a member of the constitutional convention which met at Concord to amend the constitution of New Hampshire, and was chosen to preside over its deliberations; he favored the removal of the religious-test clause in the old constitution, by which Roman Catholics were disqualified from holding office in the State, and also the abolition of any “property qualification;” he carried these amendments through the convention, but the people defeated them at the election.  In January, 1852, the Democratic State convention of New Hampshire declared for him for President, but in a letter January 12 he positively refused to permit the delegation to present his name.  The national convention of the party met at Baltimore June 1, 1852.  On the fourth day he was nominated for President, and was elected in November, receiving 254 electoral votes, while his opponent, General Scott, received only 42.  Was inaugurated March 4, 1853.  In 1856 he was voted for by his friends in the national Democratic convention for renomination, but was unsuccessful.  Upon the expiration of his term as President he retired to his home at Concord, where he resided the remainder of his life.  Died October 8, 1869, and was buried at Concord.