"If they were against slavery, they should have attempted it at all times."

There is the word "should" again. You are making a judgment of their performance, not an observation of their abilities. I agree that Congress had the ability to outlaw slavery across the nation through a Constitutional amendment. Lincoln did not have that ability, though he could, through his position as commander-in-chief, threaten slavery in certain areas.

The other problem here is that being "against slavery" did not necessarily mean being an "abolitionist." Many Americans were "against slavery" at the outbreak of the war, but did not believe that forced emancipation was wise or proper. It was not a question of legality, but a question of politics, economics, and society.

"Again, I'm not looking at motive, I commenting on the fact that IF THEY WANTED TO they could have."

There is no question that Congress COULD HAVE ended slavery...from 1787 until 1864...if there was a strong enough movement to carry 2/3 vote for an amendment.

And you are looking at motive, as you continue to comment on what they "should" have done, rather than what they were simply capable of doing. That is not only questioning their motive, but judging the value of their actions. Your comment that it was "inexcusable" for Congress to wait until 1865 to formally abolish slavery very much projects your assessment of their actions, not just their legal abilities.

I am pointing out that in 1861, no significant power in Congress desired to, or wanted to as you say, enforce national emancipation. Within four years, this changed and an amendment to the effect was passed. Considering the fact that slavery had existed on the continent for over 200 years, that 4 year period was quite remarkable.

I agree with you that it came down to a majority of legislators "wanting to" formally abolish slavery across the nation. I do not agree with you, however, that it was "inexcusable" that they did not do it sooner. If one wants to make a judgment of 19th century actions based upon modern perceptions of morality, one could just as easily (or more easily) say that it was inexcusable for the southern states to maintain slavery so long after the rest of the country voluntarily gave it up. But, I do not think such evaluations are particularly useful or productive in historical discussions.