Final answer:
One line from Abraham Lincoln's inaugural address that could have been considered radical during that time is when he emphasized the permanent nature of the Union and repudiated secession.
Step-by-step explanation:
One line from Abraham Lincoln's inaugural address that could have been considered radical during that time is when he emphasized the permanent nature of the Union and repudiated secession. This was radical because it directly challenged the belief of the southern states that they had the right to secede from the Union. By asserting the permanence of the Union, Lincoln was indicating that he would not tolerate the dissolution of the United States. This line also showed Lincoln's commitment to preserving the Union and his determination to prevent the secession of more states.