With only his law practice to sustain him, but still harboring political ambitions, Lincoln decided to make a bid for the Whig nomination in a Congress race in 1843. Much to his dismay, he failed to garner the necessary support even in his home county, and once again he was forced to wait until the next elections to realize his goal. Later that same year, he was mentioned as a candidate for governor of Illinois, but he had no interest in pursuing the position.
In 1844, Lincoln threw his political energy into the presidential race, campaigning actively for his longtime role model and third-time Whig candidate Henry Clay. Due to the third-party candidacy of former president Martin Van Buren, the Democrats were eventually swept into office on the manifest destiny platform of James K. Polk. As the strongest supporter of the annexation of Texas, Polk was able to carry expansionist Illinois, much to the chagrin of Lincoln.
Two years later, Lincoln successfully secured the Whig nomination for a seat in Congress. During the campaign, the Mexican War broke out, and became a major issue in the race. Lincoln reserved his doubts about the conflict, urging young men to volunteer rather than dissecting Polk's motivations or aims. This conservative strategy proved successful, and despite Illinois's reputation as a Democratic stronghold, Lincoln was swept into office by a sizeable majority.
Due to the progress of the war, the Thirtieth Congress did not convene until December 1847, over a year after Lincoln had been elected. By all accounts, in his single, shortened term in Washington, Lincoln failed to leave a significant mark. The only major legislative proposal he fowarded was a plan to establish the gradual and compensated emancipation of slaves in the District of Columbia, subject to free white approval.
This moderate piece of legislation was ultimately scrapped in draft form, for it displeased the abolitionists as a spineless piece of conservatism, and it infuriated the slaveholders as a radical threat to their own interests. Having lost his chance to diminish the institution of slavery, Lincoln sought to contain it, voting in support of the Wilmot Proviso, which provided that all territory gained from the Mexican War would remain free soil.
Although he had masked his initial objections to the Mexican War, and had approved the appropriation of funding for warfare, Lincoln later took the Whig Party line in condemning President Polk for what was termed an unnecessary and unconstitutional act of aggression. As one of the most vocal proponents of this censure, Lincoln made a speech on the House floor in which he pointed out that the Mexicans had made no hostile acts toward the United States and had been attacked in an area which was rightfully theirs. Most significantly, Lincoln reasoned, Polk had overstepped his executive powers "because the power of levying war is vested in Congress, and not in the President.... No one man should have that power."
Such anti-expansionist views were not well-received in Lincoln's home state, where his constituents felt they had been misrepresented by a young upstart. Lincoln did not seek re-election in 1848, and the Whigs lost their seat in Congress despite gaining the presidency under Zachary Taylor.
Most relevant to his immediate political career, Lincoln had been a vigorous champion of internal improvements, and helped the Whig cause by earning large amounts of federal funding for this purpose. In hopes of furthering his influence, Lincoln jockeyed to become Commissioner of the General Land Office, but was unsuccessful in securing the appointment. Nevertheless, he was offered a position as secretary, and later as governor, of the Oregon Territory. But with no wish to press his frontier luck again, he instead retired back to Springfield to take up his vocation as a lawyer once more.
In 1844, Lincoln had formed a partnership with a young clerk named William H. Herndon that would last until Lincoln's death in 1865. Ten years Lincoln's junior, the fire-brand Herndon was a fine complement to the more laconic Lincoln, whom he treated with a certain measure of deference as an elder. The two men worked together with a remarkable degree of good fellowship and trust, sharing all profits evenly in the absence of a zeal for record keeping.
When Lincoln returned from Washington in the spring of 1849, he resumed his law practice in earnest, continuing to build his reputation as a formidable lawyer of unyielding integrity. As his statewide profile grew ever larger, he began to take on more diversified and significant cases. He continued to travel across the state on the Eighth Circuit, and began to appear before the state supreme court regularly. He also assumed federal cases on occasion, taking on clients from such major eastern metropolitan centers as Boston, New York, and Philadelphia.
Lincoln's practice was certainly facilitated by the growth of the railroad, which he himself had helped to foster as both lawyer and statesman. Lincoln himself lobbied on behalf of the Illinois Central Railroad and helped them to obtain their charter. He was retained as their attorney thereafter, defending them successfully in their bid for immunity from county tax. Subsequently, he was forced to sue the company in order to collect his legal fee of five thousand dollars, which he was duly awarded. In another notable case, he saved the first bridge to span the Mississippi River, Rock Island Bridge, from being destroyed in the interests of riverboat traffic.
In the early 1850s, Lincoln had an extremely active law practice, representing various railroads, banks, insurance companies, merchants and manufacturers. He also took on the occasional criminal trial, once famously defending a man accused of murder by employing a lunar chart in The Farmer's Almanack to discredit the testimony of a witness. Generally, Lincoln's work was less glamorous, concerning patent suits, deeds, land registers, taxes, and simple legal advice. Although he sat in as a judge on a few occasions, he had no specific political aspirations to obtain a judgeship.
Although he himself was morally opposed to the institution of slavery, Lincoln as lawyer and politician was frequently forced to separate personal views from professional stances. As such, he represented both slaves and slave owners in courts of law, but while he was successful in gaining freedom for a slave sold in Illinois, he failed to restore a slave family to a slaveowner who attempted to reclaim them. And although Lincoln was willing to defend either side of the slave question as a prairie lawyer, the time was fast approaching when such compromises with regard to the "peculiar institution" would no longer be possible.