Well, I'm not sure blocking the funding is a good idea at all.  I understand the reasoning, which takes the soundest moral ground, and it puts me in a dilemma as I can be pretty self-righteous sometimes but this is one case where I believe politics trumps policy.  Not because the policy is wrong, to be sure, but because on past performance it won't work.  It was a memorable event, however:

    "And if we do not end this damnable war those young men will some day curse us for our pitiful willingness to let the Executive carry the burden that the Constitution places on us."

   "So before we vote, let us ponder the admonition of Edmund Burke, the great parliamentarian of an earlier day: "A contentious man would be cautious how he dealt in blood."

According to historian Robert Mann, McGovern's brief, passionate speech shocked his Senate colleagues. As McGovern took his seat, most senators sat in stunned silence. "You could have heard a pin drop," recalled John Holum, McGovern's principal staff advisor on Vietnam. As the Senate prepared to begin voting on the amendment, one senator approached McGovern and indignantly told him that he had been personally offended by the speech. McGovern replied, "That's what I meant to do.

Wikipedia - McGovern-Hatfield Amendment

Great moment.  What it basically called for, in one of several versions, for was no funds authorized by this or any other act may be obligated or expended to maintain a troop level of more than 280,000 armed forces of the United States in Vietnam after April 30, 1971.  Unfortunately if you trace back the meme that Democrats are weak on national security it will likely lead you to the same spot.  I say this as an enthusiastic supporter of McGovern at the time.  Remember the bumper-stickers of US flags with just one star and the slogan 'Don't blame me, I'm from Massachusetts?'